West Ham United have signed Portuguese defender Manuel Da Costa from Fiorentina and sent attacking-midfielder Savio Nsereko in the opposite direction.
Former Nancy and PSV centre-back Da Costa failed to establish himself in Italy's Serie A, despite a loan spell at Sampdoria, and the 23-year-old is now hoping to impress Hammers boss Gianfranco Zola.
Savio moved to the Premier League in a £9m deal during the January transfer window from Serie B side Brescia. The Germany Under-21 international is tipped to be a star but had trouble settling in England.
The Hammers will retain 50% of Savio's sell-on value and West Ham chief executive Scott Duxbury said: "This is a good deal for everyone concerned."
He added: "Although not for the want of trying, Savio has struggled to make an impact for various reasons, while Manuel is also looking for a fresh start. Had our financial situation been different we would have preferred to have kept and developed Savio.
"We will continue to look at home and across Europe for the brightest prospects as they best fit our vision for this club's future. However, we are required to make savings and our policy has always been to sell players on the fringes rather than established first-team players.
"With the fee we received for Savio and 50% sell-on together with acquiring the highly-rated Da Costa, it represented a great deal.''
Fiorentina, who have also sold Serbian midfielder Zdravko Kuzmanovic to Stuttgart for £5m, have added teenage Boca Juniors defender Ezequiel Munoz for £7m. The 19-year-old will be out for two months due to injury.