West Ham defender Nayef Aguerd, who signed for the club in June, has had successful surgery on the ankle he injured in a pre-season game against Rangers.
The Hammers added that the Morocco defender would now "continue his rehabilitation at Rush Green with the club's medical team".
Aguerd had made his debut in the previous match against Reading.
The transfer fee for Aguerd, who has 25 caps for Morocco, is the fourth-highest paid by West Ham, behind those for Sebastien Haller, Felipe Anderson and Kurt Zouma.
West Ham will begin their Premier League campaign at home to champions Manchester City on Sunday, 7 August.