West Ham's Manuel Lanzini faces four to five weeks on the sidelines due to injury, according to manager Slaven Bilic.
The Argentine joined the club on a permanent deal last month after an impressive first season on loan in the Premier League, but will now miss the start of the new campaign.
Lanzini suffered the injury while preparing for the Olympics with Argentina, and Bilic is disappointed to be missing one of his star men.
"Unfortunately that's another blow for us," the West Ham boss said ahead of their first game at the Olympic Stadium - a Europa League qualifier against Domzale.
"He was not supposed to play tomorrow anyway. He was with us in the United States during our first part of the pre-season, he stayed there and we flew back to London.
"He joined the Olympic national team, but in a friendly game against Colombia he got a kick on his knee and got injured. It's not only a kick on his knee to be fair.
"It's not a big, big injury, but he can't play for the next four or five weeks.
"I think he's going to miss the first three games of the season, which is not ideal but not that bad.
"So, we think he'll be back after the international break following the Manchester City game."
Lanzini fired six goals in 25 league games last term, helping West Ham to a seventh-placed finish.
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