London - West Ham United have signed French left-back Arthur Masuaku from Olympiakos on a four-year contract, the Premier League club announced on Monday.
The 22-year-old, capped by France at Under-19 level, will help provide cover for Aaron Cresswell, who has been ruled out for up to four months with a knee injury.
West Ham did not disclose the transfer fee, but Jack Sullivan, son of co-chairman David Sullivan, said on Twitter that the club had paid $7.8 million to sign Masuaku.
"It's a big honour for me to be part of this club," Masuaku told West Ham's official website.
"I was speaking with my agent about some opportunities, but when he told me about West Ham and also the coach (Slaven Bilic), I didn't think twice, so in my mind, it was West Ham.
"Now, to be able to play with players like Dimitri Payet, I was thinking on the way here, it's going to be crazy! I can't wait to play with him and also all the rest of the team."
Masuaku could make his debut in West Ham's Premier League opener at Chelsea next Monday.
But the former Valenciennes player is ineligible for their Europa League play-off tie with Romanians Astra Giurgiu, having already played for Olympiakos in the Champions League qualifying rounds.