Cesc Fabregas tops WhoScored's list of debuts from the weekend but you might also be surprised to see Patrick van Aanholt and Andrew Robertson in there...
We could have done practically a whole quiz on Chelsea's loanees but instead we've gone for the traditional one question per club...
1) Fredy Guarín (Colombia)
What we know about him: Guarín has just completed a remarkable season with Porto, winning four trophies including the Europa League, in which he scored five goals. A cultured midfielder, Guarín possesses a great range of passing as well as excellent awareness. Colombia will be hoping he can provide the assists for prolific club and country teammate Radamel Falcao, but Guarín can also conjure up the occasional golazo himself.
What we want to know: What's he gibbering to himself after hitting this rocket?
2) Juan Manuel Vargas (Peru)
What we know about him: Affectionately known as 'El Loco', the versatile Vargas has spent the last five seasons marauding down the wings in Serie A. He was instrumental in Fiorentina's progression to the knock-out stages of the 2009/10 Champions League, helping to eliminate Liverpool in the process. Vargas is in high demand this summer, and a move to Anfield has been reported as a possibility.
What we want to know: Will Vargas earn the right to be nicknamed El Loco?
3) Javier Pastore (Argentina)
What we know about him: He's skinny. So skinny in fact that it's his nickname - 'El Flaco'. If Chelsea or Man City are intending to spend £40million on Pastore, they're not going to get a lot of meat for their money. What they will get though is an incredibly skilful attacking midfielder with an eye for goal. When watching Pastore play for Palermo, it's easy to be reminded of ballet, although that could be because of the pink shirts rather than his grace and poise. Nevertheless, he is nimble.
What we want to know: Is he seriously worth £40million? Is anyone seriously worth £40million?
4) Sergio Aguero (Argentina)
What we know about him: Despite being a regular in Atletico Madrid's first team since 2006, Kun Aguero is still only 23. He's notched up an impressive 101 goals in 234 appearances for Atletico, including two stunning Champions League strikes against Chelsea, with whom he's been consistently linked. Aguero's desire to play at the top level has led to him revealing his intention to move clubs this summer, and when a player announces it on their official website you know they're serious.
What we want to know: What's it like to father Diego Maradona's grandson?
5) Alexis Sanchez (Chile)
What we know about him: He's currently Europe's most wanted man: Barcelona, Inter Milan, Manchester City, Manchester United and a host of other clubs are all desperate to prise the speedy winger from Udinese this summer. After helping his team reach the Champions League places in Serie A - including scoring four goals in a 7-0 hammering of Palermo - Sanchez has his pick of possible destinations.
What we want to know: Sanchez isn't just a one-season wonder - his performances for Chile have attracted admirers since the qualifying stages of the 2010 World Cup. With all considered, why wasn't he snapped up by someone last August when he would've cost much, much less?
6) Edinson Cavani (Uruguay)
What we know about him: Cavani goes into the Copa America on the back of his most successful season at club level. After joining Napoli in July 2010, he hit a personal best of 26 goals to become the highest league goalscorer in a single season for his new club. Inevitable links to Manchester City soon followed for 'El Matador', but it's likely that he'll lead Napoli in their first Champions League campaign.
What we want to know: Is he the long-term replacement for Diego Forlan? And why is he still wearing braces at 24?
7) Carlos Tevez (Argentina)
What we know about him: To use the Alan Hansen dictionary: Power...Aggression...Awesome. Tevez is a beast of a player and can score goals at any time, be it through his relentless harrying of defenders or a sublime free-kick (see 17 May v Stoke). Winner of the South American Footballer of the Year in 2003, 2004 and 2005, Carlito is happiest when he's at home. Unfortunately for Manchester City fans, Tevez's desire to be spend more time with his family is only going to be strengthened by a prolonged stay in Buenos Aires.
What we want to know: How do you keep him happy? It's no wonder his favourite goal celebration involves sucking on a dummy. If only he'd stop spitting it out.
8) Paulo Henrique Ganso (Brazil)
What we know about him: One of the stars of the current Santos team and the latest in a long line of gifted Brazilian attacking midfielders. At only 21 years of age, Ganso is already a commanding presence and can dictate the flow of play with his wonderful left foot. Brazil will be looking to him to provide the assists for Neymar as well as contributing a goal or two himself. An outstanding prospect and hopefully one to watch for years to come.
What we want to know: Does Ganso's rise signal the end for Kaka?
9) Neymar (Brazil)
What we know about him: Following a low-key 2010 World Cup and a great deal of criticism over Dunga's pragmatic tactical approach, the most important thing Brazil needed was a new hero. New coach Mano Menezes turned to Neymar, who duly responded with a goal on his debut against the USA. Five caps, two goals against Scotland, and a hell of a lot of Chelsea speculation later, Neymar will be looking to prove the hype in Argentina.
What we want to know: Is he actually as good as those who came before him? Or do we all just want him to be?
10) Lionel Messi (Argentina)
What we know about him? No list of players to watch would be complete without the inclusion of Messi. After another incredible season for Barcelona, the diminutive Argentine returns to his homeland to spearhead his countr''s attack at the Copa America. With no goals at the 2010 World Cup, the only red mark against Messi's name when it comes to debating the greatest player of all time is that he is yet to win a major tournament with Argentina.
What we want to know: Playing in a team inferior to Barcelona, can Messi still produce his very best, and will that be enough to claim silverware for the hosts?