5 costliest January transfers in history

#4 Diego Costa (£57m, Chelsea to Atletico Madrid, 2018)

Costa returned to Atleti in 2017

It's safe to say Diego Costa caught the public eye in England. He enjoyed three roller-coaster seasons with Chelsea and was loved and hated by fans alike. Costa won two Premier League titles, but his explosive personality eventually paved his way out.

Costa won the league with Antonio Conte, but their relationship turned sour towards the end. Conte texted Costa in the summer that his services won't be required for the upcoming season. A return to Atletico was always on the cards, and January was when it occurred. He was facing injury and fitness issues, hence the transfer happened later on.

He has not rekindled his Atleti form from previous years, however. His goals brought the LaLiga title in 2014 when he was unstoppable. Currently, he is sidelined, but expect him to make headlines soon. That's just the way he is, for better or worse.