Where are they now? The best teenage XI in Europe from 2009/10

Jadon Sancho's career continues to go from strength to strength and talk of a blockbuster summer move to Manchester United is gathering pace. In just two full seaons as a professional, the Borussia Dortmund wonderkid is already considered among the best in the world.

Whether his career continues at the same startling trajectory remains to be seen. Some prospects fulfil their potential, while others struggle to stay disciplined and eventually watch their careers fizzle out.

With that, we have taken a trip down memory lane to the 2009/10 campaign, the first season we received Opta data, and unearthed the best WhoScored rated teenage XI from Europe's top five leagues to see how their careers have transpired over the last decade.

Some players in the XI, as revealed below, have gone on to become the best in the world, while others have not. It serves as a huge warning to the likes of Sancho, who are starting on the same path. 

We have also partnered with the leading transfer valuation website, Transfermarkt (TM), to provide each player's market value at the end of the 2009/10 campaign. Even with transfer fees set to tumble as a result of the coronavirus pandemic, as TM have accounted for in their latest valuation update, it's unlikely you will ever see top rated teenagers with transfer valuations as low as they were a decade ago.

Goalkeeper: David de Gea (Atletico Madrid) - 6.75 rating / £6.3m TM value

David de Gea started the 2009/10 campaign as back-up to Sergio Asenjo at Atletico Madrid but took over as the club's first-choice goalkeeper in January 2010 and never looked back. At the age of just 19, De Gea only made one error that directly led to an opposition goal in 19 LaLiga appearances in 2009/10 and averaged 3.5 saves per game.

After just one full season as Atletico No.1, De Gea earned a blockbuster move to Manchester United in 2011. His first few seasons at United were difficult to say the least and his reputation flatlined as a result. However, De Gea eventually came good on his potential and was regarded as the best goalkeeper in the world for several years. In fact, his TM value peaked as high as £63m in 2018. A tough two-year period, however, has seen De Gea's valuation fall to £36m as of April.

Right-back: Cesar Azpilicueta (Osasuna) - 7.04 rating / £6.3m TM Value

Cesar Azpilicueta was a first-team regular for Spanish side Osasuna from the age of 17 and had already racked up 65 top-flight appearances by the time the 2009/10 season rolled around. A return of 3.1 tackles per game and hugely impressive success rate of 84.4% was certainly enough to capture Marseille's attention in the summer of 2010. After two campaigns in France, Chelsea came calling for the Spanish right-back and he has been a pillar of consistency for the Blues ever since, ranking fourth for the club on the all-time appearance list in the Premier League.

The Chelsea captain has only missed two league games this season but with Reece James coming through the ranks at Stamford Bridge, Azpilicueta should expect reduced playing time going forward. His TM valuation peaked as much as £40m in 2018 and now sits at £21.6m.

Centre-back: Nicolas Nkoulou (Monaco) - 6.96 rating / £4.05m TM Value

Nicolas Nkoulou's breakout season for Monaco came during the 2008/09 campaign and he further established himself as a highly-rated young centre-back the following season as a 19-year-old. In his formative years he loved to rob opponents of possession. In 2009/10 he averaged 3.3 tackles per game and it remains his highest ever return in a single campaign a decade on.

After another season at Monaco, Nkoulou moved to Marseille for European football and after five years for Les Phoceens he joined their rivals Lyon as a replacement for Barcelona-bound Samuel Umtiti. Things didn't pan out as expected for Nkoulou at Lyon and after a loan stint at Torino he joined the Serie A outfit permanently in 2018. The former Cameroon international was linked with a move to Arsenal in January 2019, around the time his TM Value peaked at £13.5m.

Centre-back: Mamadou Sakho (PSG) - 6.84 rating / £8.55m TM Value

Mamadou Sakho was regarded as one of the best young defenders in Europe when he emerged on the scene for boyhood club Paris Saint-Germain in 2007 but was forced to leave to further his development when the Qatari-millions started signing the best rather than promote from within. Sakho joined Liverpool in 2013 but only ever really showed flashes of potential, as injuries and a controversial drugs test in 2016 effectively ended his career at Anfield.

That tallies up with Sakho's peak TM valuation, which stood at around £17.1m the season he joined Liverpool. Thereafter it gradually dropped and injuries have continued to stifle his career since joining Crystal Palace in 2017. His current TM valuation (£8.55m) is actually the same as it was 10 years ago.

Left-back: Davide Santon (Inter) - 6.92 rating / £9m TM Value

Davide Santon was a two-time Serie A champion and Champions League winner by the time he was 19 and in hindsight that may have actually been the worst thing that could have happened to him. Rather than build on an immense start to his career, Santon has jumped from club-to-club. It was considered a coup for Newcastle when they signed the versatile full-back in 2011 and while he was a first-team regular at St. James' Park for most of his time there he flattered to deceive during his four-year stint at the club. In fact, his TM valuation never even reached the £10m mark, first reaching £9m after Inter won the treble in 2009/10.

Santon has only ever been a bit-part player since leaving Newcastle to return to Inter in 2015 and that has continued at Roma for the last two years. With only seven league starts under his belt for Roma in 2019/20, his current TM valuation stands at just £3.5m - only twice in the last decade has it been lower.

Right wing: Thomas Muller (Bayern Munich) - 7.40 rating / £9m TM Value

As far as breakthrough seasons are concerned, Thomas Muller's was certainly impressive. He played a direct hand in 19 goals in 34 league appearances for Bayern Munich in 2009/10. Unlike anyone else in the top rated teenage XI from the 2009/10, Muller has remained at the same club his entire career.

His TM valuation really rocketed during Pep Guardiola's time at the club when Muller enjoyed his best ever goalscoring campaign in the Bundesliga. The Germany international finished the 2015/16 campaign with 20 goals, seven more than he has managed in any other league season in his career, and his TM valuation peaked at £67.5m. A tough 2018/19 season saw Muller's TM valuation plummet, as his time at Bayern looked to be coming to a close. It currently stands at £22.95m, its lowest since 2012, but he has been in exceptional form this term. Coupled with a new contract extension, it might even go back in the right direction come the end of the season.

Central midfield: Toni Kroos (Bayer Leverkusen) - 7.59 rating / £10.8m TM Value

After being eased into life in the Bundesliga in the first year of his two-season loan stint at Bayer Leverkusen, Toni Kroos really flourished in his first full season in 2009/10. Aged 19 at the start of the season, Kroos went on to score nine league goals and that return remains his best ever in a single league campaign in his career. Kroos' role in midfield has of course changed dramatically since then, as he is now considered a master of controlling possession rather than a goalscoring midfielder.

After scoring nine goals and registering as much assists in 09/10, Kroos returned to Bayern before surprisingly being sold to Real Madrid in 2014. Kroos won the Champions League three times in a row with Madrid, the last coming in 2017/18 where his TM valuation peaked at £72m. Kroos hasn't quite been the same since then and his current TM valuation is at its lowest since he first moved to Spain.

Central midfield: Miralem Pjanic (Lyon) - 7.10 rating / £11.25m TM Value

An eye-catching breakout year for Miralem Pjanic at the age of 17 earned him a move to Lyon straight away in the summer of 2008. His first season at Lyon was steady but in 2009/10, at the age of 19, he really flourished. Pjanic finished that season with 10 assists and six goals. Only on two other occasions since then has the Bosnian midfielder reached double figures for assists in a single league campaign.

Roma came calling shortly afterwards before Juventus snapped up the midfielder from their Serie A rivals in 2016. Pjanic has been highly rated as a midfielder capable of dictating the tempo of a game but always considered just outside the elite bracket. For 12 months from December 2018 his TM valuation peaked at £63m but now his reputation has dipped and Juventus are looking to offload the 30-year-old. His TM valuation currently stands at £46.8m, though potentially being lined up by Chelsea and Barcelona suggests he is still well thought of in Europe.

Left wing: Eden Hazard (Lille) - 7.21 rating / £12.6m TM Value

Eden Hazard emerged from Lille's academy properly in 2008/09 but it wasn't until a year later that he started to turn heads. The Belgium international finished his second full campaign as a professional with five goals and eight assists. In 2011/12, when Hazard was just 20, he finished the season with 20 goals and 16 assists for third-place Lille. Those displays earned him a high profile move to Chelsea and during his seven-year stint at Stamford Bridge he developed into one of the Premier League's best ever players.

Hazard finally relented to Real Madrid's long-standing interest and moved to Spain last summer in a blockbuster deal worth up to £150m. Madrid captured Hazard's services during the time when his TM valuation was at its peak (£135m). His first season at Madrid, however, has been a nightmare and has led to a huge slump in his valuation. Various injuries have limited Hazard to just nine league starts in 2019/20 and he is now valued at £72m.

Striker: Alexandre Pato (AC Milan) - 7.53 rating / £31.5m TM Value

When Alexandre Pato broke into the AC Milan first-team midway through the 2007/08 campaign at the age of 18, there was genuine belief the Serie A giants had unearthed the next Brazilian superstar. He reached double figures for goals in his first three full league campaigns for Milan, including a haul of 12 in 2009/10, and looked destined for big things. His TM valuation peaked at £31.5m during 09/10, by far and away the top valued player in our teenage XI that season.  

An unfortunate run of muscle injuries during his formative years, however, proved detrimental to his career later on. After 2010/11, when he scored 14 league goals, he was never the same. He managed just 10 league starts from 2011 to 2013 before returning to Brazil for three years. A surprise move to Chelsea in January 2016 offered him one last chance to salvage his career but it wasn't to be. Since then he has played in Spain, China and is now back in Brazil. His current TM valuation is just £4.32m, further highlighting what has been a thoroughly disappointing career since his early breakthrough.

Striker: Mario Balotelli (Inter) - 7.34 rating / £13.5m TM Value

Like Pato, Mario Balotelli's career has been hugely frustrating. It started with a bang and is on course to end with a whimper. He was billed as 'the next' Adriano when he broke onto the scene at Inter with nine goals and five assists in 2009/10 despite only starting 13 league games. In many ways he has endured a similar career to Adriano: a hugely exciting prospect that eventually fell by the wayside.

His time at Manchester City was full of ups and downs. His only Premier League assist helped City win their first ever Premier League title and his TM valuation peaked that summer, hitting £28.8m. But the Italian quickly ran out of chances and was sold to AC Milan six months later in January 2013. As his relationship with City soured, so did his TM valuation. Just as quickly as it went to £28.8m to fell to just over £20m by the time he returned to Italy. A productive 18-month stint at Milan led to a surprise move to Liverpool but that was again short-lived. Since then he has again played for Milan and endured spells at Nice, Marseille and now hometown club Brescia, whom are reportedly set to release the troublesome forward. His TM Valuation is now only £4.95m.