Arsenal defender William Saliba is set to miss six weeks at St Etienne.
Saliba, who has been loaned back to French side Saint-Etienne, underwent an op on an adductor muscle injury.
The centre-back, 18, has been battling the issue since the end of last season.
Saliba did make an appearance in a pre-season friendly against Newcastle earlier this month but missed the first game of the Ligue 1 season last weekend, a 2-1 win at Dijon.
St-Etienne coach Ghislain Printant said: "Saliba had an operation earlier this week.
"We will take our time with his return."
