Most players who are still in the Under-21 stage more or less are looking for a chance to get into the first team, but there are some players that are so good and talented that they are worth as much or more than the top players in the game.
Here are the top 10 most valuable U-21 players, according to a Soccerex report.
10. Eder Militao - €54.6 Million
Eder Militao is just under the age bar for this list and has made a big money move to Real Madrid in this summer. The Spanish club, as part of its summer overhaul, paid €54.6 million euros to bring the player from Porto. He will be expected to refurbish the defence and help them close the gap to Barcelona.
9. Christian Pulisic - €57.2 Million
Christian Pulisic confirmed his move to Chelsea in the January transfer window, with the Blues avoiding the transfer ban they are currently under. The American cost a solid €64million for the Blues to bring him from Borussia Dortmund where he scored seven goals. His current worth is €57.2m.
8. Vinicius Junior - €60.2 Million
Vinicius Junior moved to Real Madrid last season, and following a not so start for the club in the season, the player was given a number of chances to prove his worth. He made a total of 31 appearances and scored four goals for the team. The 18-year-old is currently valued at €60.2million.
7. Gianluigi Donnarumma - €67.9 Million
Gianluigi Donnarumma may be only 20-years-old but he has already been playing regularly for four years now for AC Milan. The goalkeeper has been in top form for the Italian club and keeping more 50 clean sheets in all competitions so far in his career.
He is currently valued at €67.9million.
6. Joao Felix - €71.8 Million
Joao Felix is all of 19-years-old and he already has a transfer price tag of over €100million to his name. Atletico Madrid were so impressed with the player that they chose to pay the release clause of €126million to bring the player from Porto.
Although he is currently valued at €71.8m, Atletico's decision to make him their biggest transfer also made him the second most expensive teenager.
5. Trent Alexander-Arnold - €73.6 Million
Trent Alexander-Arnold had a fantastic season for Liverpool, and helped his team win their sixth Champions League title. Although the Reds missed out on the Premier League title, his right-back credentials have ensured that he is valued at a very high €73.6million, not that Liverpool would in any hurry to sell him to anybody.
4. Kai Havertz - €74.2 Million
Kai Havertz may be only 20-years-old, but he has been a regular at Bayer Leverkeusen for three seasons now. Last season was particularly phenomenal for the youngster, having scored 20 goals in all competitions, and becoming the teenager with most goals in a Bundesliga season in the process.
It is no surprise that his market value is right now at €74.2million.
3. Matthijs de Ligt - €74.5 Million
The Ajax captain had a fabulous campaign last season, helping the team win the league title and also reaching the Champions League semifinals. Matthijs de Ligt has been the subject of a number of clubs but wherever he goes to, they would have to pay upwards of his current market value of €74.5million.
2. Jadon Sancho - €120.3 Million
Jadon Sancho will be forever be grateful for choosing to leave Manchester City and joining Borussia Dortmund. The 19-year-old Englishman had a great season for the German club, taking them within reach to the Bundesliga title with 12 goals in the league.
If a club has to tempt Dortmund, they would have to at least match his market value of €120.3 million.
1. Kylian Mbappe - €261.6 Million
Kylian Mbappe became the most expensive teenager when Paris Saint-Germain paid €135 million to Monaco for the French international. He has since just put in excellent performances for both club and country, even winning the World Cup and scoring in the final.
As such, it is no surprise that his current market value is €261.6m, having scored nearly 40 goals in all competitions last season.
Here are the top 10 most valuable U-21 players.