The 2018 World Cup is almost upon us. Official roster have been released. The daily countdown has dipped into single digits. The greatest sporting even on earth is near.

And every four years, it doubles as a proving ground. Dozens of youngsters will make their World Cup debuts in Russia. Some won’t see the field. But others will announce themselves to millions around the globe. They’ll kick-start successful careers, or further their ascent into the sport’s elite.

[Yahoo Sports’ 2018 World Cup preview hub]

For a look at those players, we’ve decided to set the cut-off at 23 years old. We’ve compiled a list of the 40 best World Cup participants who’ll be under the age of 23 when the tournament kicks off. (Note: That means a player like Colombian center back Davinson Sanchez, who’ll turn 23 two days before the World Cup opener, is ineligible.)

The following rankings are not based on future potential, but rather on present-day quality and impact. It’s essentially the same criteria as our big 2018 World Cup top 100 list, except with an age restriction. As you’ll see, though, even with that age restriction, there was no shortage of talent to choose from.

Here’s the list:

1. Kylian Mbappe, F, France/PSG (19)

Of the 736 players at the World Cup, Mbappe is the second-youngest. He’s also, by our estimation, the ninth-best. That’s insane.

2. Gabriel Jesus, F, Brazil/Manchester City (21)

Only just turned 21, but has already beaten out prime-age stars for the starting striker spot with Brazil and at Man City.

3. Ousmane Dembele, M/F, France/Barcelona (21)

Even younger than Jesus, and, like Mbappe, already a $100-plus-million man. He might not get in France’s loaded 11, but should at least be a field-stretching option off the bench.

4. Dele Alli, M, England/Tottenham (22)

With three very productive seasons at Spurs already under his belt, easy to forget he’s a (young) 22. He should start as one of England’s two box-to-box midfielders.

5. Thomas Lemar, M, France/Monaco (22)

Seems closer to the finished product than several of the players immediately below him on this list – which makes his 2017-18 regression slightly worrying. Or, perhaps his presence here is a good reminder that he still has room and time to grow.

6. Marco Asensio, M/F, Spain/Real Madrid (22)

Has been valuable to Madrid and Spain as an energizing, counter-attacking substitute and spot-starter. That’s what he’ll be at the World Cup. But he has the talent to be more than that.

7. Niklas Sule, D, Germany/Bayern Munich (22)

Has had a grown man’s body every since he was a teenager, and has developed the technical ability to match it. Broke into the Bayern team as Jerome Boateng’s deputy, and could do similarly with the national team.

8. Lucas Hernandez, D, France/Atletico Madrid (22)

The Atleti academy product doubled his career La Liga appearance total in 2017-18, and looks like the heir apparent to either Felipe Luis or Diego Godin. And he could eventually be better than both of them. Can play on the left or in the center of defense.

9. Goncalo Guedes, F, Portugal/Valencia (21)

Moved to Valencia on loan from PSG to get first-team minutes, and made the most of them. Likely won’t start for Portugal, but should be Fernando Santos’ down-a-goal wild card.

10. Timo Werner, F, Germany/RB Leipzig (22)

Would seem to have Germany’s starting striker spot nailed down.

11. Marcus Rashford, F, England/Manchester United (20)

If he were getting regular playing time at United, it’d be really tough for Gareth Southgate to keep him on the England bench. His raw pace and skill are clear for all to see.

12. Hirving Lozano, F, Mexico/PSV Eindhoven (22)

His first season in Europe was a resounding success. Can he replicate that success on the biggest stage of all?

13. Benjamin Pavard, D, France/Stuttgart (22)

If you hadn’t heard of Pavard until he was named in France’s 23-man squad – or until now – you certainly weren’t alone. But he’s the picture-perfect new-age defender. He can player center back in a four, right center back in a three or right back in a four. He can slot into a holding midfield role. His ability to read the game, for a 22-year-old, is uncanny. And he’s both elegant and decisive on the ball.

14. Christian Pavon, F, Argentina/Boca Juniors (22)

Arguably the best under-23 player based in South America, and certainly the best at the World Cup.

15. Alvaro Ordiozola, D, Spain/Real Sociedad (22)

A surprise Spanish call-up, the right back had a breakout campaign at Sociedad.

16. Giovani Lo Celso, M, Argentina/PSG (22)

An offensive-minded midfielder who’s passing can be utilized anywhere in the center of the park. Who could start next to Javier Mascherano or Lucas Biglia at the base of midfield for Argentina.

17. Andreas Christensen, D, Denmark/Chelsea (22)

Christensen found it difficult to break into Denmark’s team throughout qualifying, but an injury to Andreas Bjelland has presented him with an opportunity. His distribution from the back is his best quality.

18. Trent Alexander-Arnold, D, England/Liverpool (19)

Who could’ve foreseen this? Alexander-Arnold at the World Cup as a teenager? Surely not even Jurgen Klopp. But the Liverpool lad absolutely belongs, and would start at right back for more than half of the teams in Russia.

19. Maxi Gomez, F, Uruguay/Celta Vigo (21)

The Edinson Cavani heir.

20. Julian Brandt, F, Germany/Bayer Leverkusen (22)

Hasn’t lived up to the hype of his teen years … yet. But Joachim Low apparently thinks he’s better than Leroy Sane, and Sane wouldn’t been No. 2 on this list, sooo …

21. Presnel Kimpembe, D, France/PSG (22)
22. Wilfred Ndidi, M, Nigeria/Leicester City (21)
23. Youri Tielemans, M, Belgium/Monaco (21)
24. Alex Iwobi, M/F, Nigeria/Arsenal (22)
25. Andre Silva, F, Portugal/AC Milan (22)
26. Manuel Akanji, D, Switzerland/Borussia Dortmund (22)
27. Amine Harit, M, Morocco/Schalke (20)
28. Nahitan Nandez, M, Uruguay/Boca Juniors (22)
29. Aleksandr Golovin, M, Russia/CSKA Moscow (22)
30. Kelechi Iheanacho, F, Nigeria/Leicester City (22)
31. Renato Tapia, M, Peru/Feyenoord (22)
32. Ruben Loftus-Cheek, M, England/Crystal Palace (22)
33. Denis Zakaria, M, Switzerland/Borussia Monchengladbach (21)
34. Ruben Dias, D, Portugal/Benfica (21)
35. Ismaila Sarr, F, Senegal/Rennes (20)
36. Rodrigo Bentancur, M, Uruguay/Juventus (20)
37. Nico Elvedi, D, Switzerland/Borussia Monchengladbach (21)
38. Lucas Torreira, M, Uruguay/Sampdoria (22)
39. Andrija Zivkovic, M, Serbia/Benfica (21)
40. Kasper Dolberg, F, Denmark/Ajax (20)

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Henry Bushnell covers global soccer for Yahoo Sports. Have a tip? Question? Comment? Email him at henrydbushnell@gmail.com, or follow him on Twitter @HenryBushnell, and on Facebook.

World Cup coverage from Yahoo Sports:
• 2018 World Cup preview hub
• From Messi to Henderson, the top 100 players at the World Cup
• Top 25 players who aren’t going to Russia
• Group previews: A | B | C | D | E | F
• FC Yahoo Mixer: With U.S. out, who to root for?