West Ham have signed left-back El Hadji Malick Diouf from Czech champions Slavia Prague in a deal worth £19m (€21.9m).
Diouf helped Slavia win their 22nd domestic title last season, as they finished 16 points clear of Viktoria Plzen, taking 90 points from 35 matches.
The 20-year-old – who won the first of his four senior caps for Senegal last year – played 27 league games in 2024-25, contributing to eight clean sheets.
Diouf, who has also played at left wing-back, has signed what West Ham described simply as a "long-term" contract.
"I'm really happy to be here and to make a progression for my career. I'm looking forward to working hard and joining my new team-mates," Diouf said.
"There were a lot of teams [who wanted to sign me], but I chose West Ham first, and I spoke with Graham Potter, and it was a good plan for me.
"Everyone wants to come here to play in the Premier League. I think it is a dream for everyone.
"When they are here, they want to make everything good. I think they also have the personality to play here, and if you are young, you want to continue your progression."
Diouf is West Ham's second signing of pre-season, after Jean-Clair Todibo's loan move became permanent for £36.3m (€42.5m).
The Hammers have let Vladimir Coufal, Kurt Zouma, Michail Antonio, Danny Ings, Aaron Cresswell and Lukasz Fabianski leave as free agents, while Mohammed Kudus was sold to rivals Tottenham for £55m.
