The top clubs spend big to bolster their squads and replace those underachievers, while sides fighting to survive hunt for bargains and pick up the scraps.
Players with the calibre of Zlatan Ibrahimovic, Henrikh Mkhitaryan and Ilkay Gundogan have already arrived in England to showcase their talents.
But there are many who have failed to shine yet gone onto bigger and better things, and Express Sport looks at those who some sides wish they never let slip.
Paul Pogba is the name on every Manchester United fan’s lips this summer, but he could yet prove to be a rarity in the ‘let go too soon’ genre.
Jose Mourinho is trying to bring him back to Old Trafford after the club let the France international leave for Juventus before rising to the very top level.
Another United will certainly regret having sold is Gerard Pique, as the Barcelona defender left for just £5million before cementing himself in one of Europe’s most successful ever teams.
At Stamford Bridge, Chelsea have certainly been susceptible to flogging future stars, with the likes of Kevin De Bruyne, Romelu Lukaku and Daniel Sturridge all prospering elsewhere.
Manchester City can also include themselves in the category for Sturridge, as the Liverpool and England striker has proven when fit he is deadly.
Outside of the Premier League too, AC Milan must rue the premature sale of Pierre-Emerick Aubameyang, with the Borussia Dortmund goalscorer now one of Europe’s hottest talents.
Have a look at the list in full in our video above…