Ranking the 20 Best Under-21 Summer Transfer Window Prospects

The January transfer window might still be faintly visible in the rearview mirror and the wounds still fresh for some clubs, but attentions have already turned to a summer of opportunity.

Have no doubts that clubs are refining their shortlists ahead of the more traditional time to do business, and talented young players are always going to be of interest.

Here, B/R has compiled 20 remarkably gifted players who will still be under the age of 21 by the time June 2017 rolls round and who will surely be of interest to the world's elite clubs.

They're ranked in accordance with the potential, with the best situated at the top.

20. Issa Diop, Toulouse

Diop's a physical, strong centre-back whose passing game has improved a lot this season. There's work to be done, but there are parallels between Diop and Kurt Zouma.

19. Adam Ounas, Bordeaux

FourFourTwo have credited Manchester United with an interest with Ounas, who is an exciting young Algerian winger plying his trade for Bordeaux.

18. Ante Coric, Dinamo Zagreb

Coric has the feet and skillset to dazzle defenders, and he does so with frequency. It's time he made the step up; there's only so much you can learn from nutmegging Croatian league defenders.

17. Alban Lafont, Toulouse

Lafont is AC Milan's answer to Gianluigi Donnarumma—a local-born young goalkeeper who debuted at 17 and now commands the first-team gloves. He's aerially dominant and eases pressure on his defence well.

16. Dominic Solanke, Chelsea

What seems like a contractual stand-off between Solanke and Chelsea has seen the player's stock plummet, per the Daily Star's Alex Harris, and with his contract up at the end of the season, he might well be a free agent in July.

Sixteen-year-old Ryan Sessegnon has had quite the breakthrough season. Suddenly a key part of a very good Fulham side, he's clocked 15 senior appearances and has chipped in with four goals.

The Cottagers can be quite slow and patient with their buildup play, so someone like Sessegnon, to whom they can fire out the ball so he can attack the flank with verve, is key. His crossing's a bit hit-and-miss but always seems to create danger even if it doesn't go exactly where it was aimed.

Team-mate Stefan Johansen told the Evening Standard that he believes Sessegnon could become one of the world's best left-backs, and given his rapid progress, it wouldn't be a surprise if an Arsenal or a Liverpool snapped him up this summer.

Jorge Mere is a rare breed of centre-back, combining size and power with good defensive acumen and brilliant ball-carrying skills.

His assuredness in bringing the ball out of defence to create passing lanes belies his 19 years, and he's also shown excellent one-on-one skills when defending. His bear-like physique makes him a big threat in the penalty box, too.

Players like this don't hang around at clubs like Sporting Gijon long. Expect Mere to be linked with the entire Spanish top order this summer.

Jesus Vallejo has impressed greatly during his loan spell with Eintracht Frankfurt this season, alerting a number of clubs to his ability—including his parent team Real Madrid.

With Pepe ageing and centre-back soon to emerge as a need, some assumed Los Blancos would utilise Vallejo as a back-up to Raphael Varane and Sergio Ramos in 2017-18, but the player himself has poured a bit of cold water on those suggestions.

"It's not confirmed that I have to go back [to the Bernabeu]," Vallejo told Frankfurter Rundschau (h/t ESPNFC). Should he be available for another loan or perhaps a transfer with a buy-back, expect most of Spain and half of Germany to place an offer.

Might this finally be the summer Youri Tielemans leaves Belgium?

A prodigious talent who made his debut at the absurdly young age of 16, he's thought of highly by the Football Manager generation but is yet to make the transfer splash expected.

Now 19, he's bagged more than 100 senior appearances for Anderlecht and could finally be in the right mindset for a big move. Clubs in need of a free-kick maestro whose long-range passing can make a stadium weep need simply apply within.

If you're one to place stock in genes or DNA, you'll love Nikola Vlasic: He's a professional footballer for Hajduk Split, while his sister is Croatia's top high jumper and their father is her coach.

Nikola reportedly rejected a move in 2016 so his sister, Blanka, could focus on the Rio 2016 Olympics, in which she achieved a bronze medal. Now that's over, though, expect Nikola to be the subject of more enquiries.

He's a key man for Hajduk and has laid on four league assists so far this season, per Transfermarkt. His ability to lift perfectly weighted through balls in behind defences has left many opposing managers flummoxed.

"My future is here and I'm enjoying it," Moussa Dembele told TV reporters (h/t Metro) after Celtic's win over St. Johnstone at the weekend, but that statement is fooling no one.

The Frenchman's incredible season so far, inclusive of a whopping 23 goals, has turned many a head. He caused a storm on transfer deadline day by getting a plane to London...only to see someone about a knock to his knee that had been bothering him.

Dembele might be happy in hoops, but sooner or later someone will offer Celtic a gargantuan sum for his services, and it could easily be this summer.

The big problem buying clubs face is determining exactly how good he is. You don't have to be world-class to score a truckload in Scotland, and Dembele has fluffed his lines a few times in the Champions League.

Mikel Oyarzabal broke into the Real Sociedad first team last season, making 16 starts. This term he's already bettered that mark, with 19 under his belt, as he has become a permanent fixture under Eusebio Sacristan.

A speedy, dangerous winger, the Basque native showed last season he has an eye for goal (scoring six), and this season he has been generous in his creativity (creating five and counting, per WhoScored). At just 19 years of age, there's room for so much improvement, and you can bet the big clubs will start swirling soon.

Kelechi Iheanacho doesn't appear to retain the trust of Pep Guardiola, and that's a big problem. Since Gabriel Jesus joined Manchester City, the Nigerian hasn't really featured, and he didn't even make the bench for the last squad.

With Sergio Aguero and Nolito also in the rotation for a striking role, it seems clear that Iheanacho—nominally third or fourth choice at this point—will need to leave to find regular football and continue developing.

If any club needs a natural No. 9 with a superb goalscoring return and brilliant movement in the box, let Pep know. He might be looking to sell.

Franck Kessie is a name you are going to hear a lot about over the next five months or so, as every club under the sun appears to have varying degrees of interest.

Chelsea's bids were knocked back in January, but once Kessie had departed for the Africa Cup of Nations, the story cooled off a little. But this week a flood of rumours regarding a sale to Roma arrived, with Atalanta captain Alejandro Gomez telling Radio Closs Continental he believed the deal had been struck.

It's unlikely to get any clearer any time soon so speculation will continue. What we can say is that Kessie is worth the attention; he's a dynamic, goalscoring box-to-box midfielder who can dominate physically and adopt tactical instruction.

It hasn't quite gone to plan for Ruben Neves so far.

He made his FC Porto debut at 17 years and five months, became the youngest player ever to score for them in the league and collected two senior Portugal caps fairly quickly. 

But a couple of years on, Neves is 19 and hasn't really broken into the FCP team properly. It might be the hierarchy are tempering his exposure to senior football on purpose, and injuries have played a part in his lack of traction, but he isn't the star people expected just yet.

That hasn't stopped tabloids linking him with big-money moves, though. In October The Sun reported Liverpool and Chelsea still like him, and the prices being talked about are in the region of £35 million.

"Where would I play in Europe? My answer is always PSG," Thiago Maia told reporters this week (h/t TalkSport). "Why not Barcelona or others? Because Marquinhos is over there [at PSG], and he's my friend."

OK then...

Maia's unique way of choosing his next destination is quite appropriate, as he's a unique player. Few can claim to boast his blend of deep-lying playmaking ability and tough tackling, and his left foot can shape a pass in the same way some of the best do.

Chelsea were strongly linked to him last summer, but it seems as though they'll have to fight tooth and nail to land him in 2017. Maybe sign Marquinhos, then ask?

According to Squawka, only one teenager has been directly involved in more goals than Kylian Mbappe (nine) this season, and that's Ousmane Dembele (12). 

What makes that more impressive is that Mbappe has played approximately half the minutes (609) that Dembele (1123) has. It's fair to say he's making the most of his chances on the pitch.

Mbappe is a versatile forward who can play wide or up top and has intrigued this season thanks to his languid, oddly effective dribbling style. B/R's Dean Jones credited Arsenal with an interest in December, and it wouldn't surprise to see plenty of clubs follow suit.

In December, Gabriel Barbosa's agent revealed his client is unhappy at Internazionale and could leave if things don't improve, per the Daily Mail. Fast-forward to February and things haven't got much better.

With just 35 Serie A minutes to his name this season, it's understandable why he might be upset. Inter have changed managers this season, and things haven't really improved for the Brazilian under Stefano Pioli.

Barbosa, nicknamed "Gabigol" for obvious reasons, is an incredible raw talent who possesses a similar playing style to Luis Suarez: voracious, hardworking and versatile. If Inter don't want to hone his talents, there are tens of clubs who will.

The Manchester Evening News reported that while Manchester United are still infatuated with Antoine Griezmann and will go all out to sign him this summer, there's another striker, by the name of Kasper Dolberg, on their radar, too.

You wouldn't blame any top club for keeping a beady eye on the progress of the Dane, who has managed an impressive nine goals and four assists from 17 Eredivisie starts for Ajax this season, per WhoScored. He's also been something of a wondergoal machine, often netting after mazy dribbles or with acrobatic efforts. 

These players are ranked in accordance with their potential or ceiling, so it's only right that Ousmane Dembele of Borussia Dortmund claims the No. 1 spot.

His latest appearance for BVB showcased once again just how incredible his raw talent is. Skipping past two markers with consummate ease, he steadied himself before lifting a beauty of a cross in for Pierre-Emerick Aubameyang to head home. The goal was enough to win a crucial game against RB Leipzig.

The Frenchman's speed, dribbling ability and willingness to go inside and out make him a nightmare for full-backs to deal with. He seems destined to become one of the world's best players.

This hasn't exactly gone unnoticed. Bayern Munich rivalled Dortmund for the 18-year-old's signature last summer, while the player has admitted he'd like to play for Barcelona, per the Mirror. Thomas Tuchel would be loath to lose him this summer, but it's not exactly out of the realms of possibility.

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All statistics via WhoScored.com