Arsenal’s £27million summer signing William Saliba will miss six weeks of the season after having surgery.
Saliba, who has been loaned back to French side Saint-Etienne, underwent an operation 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.”
Gunners boss Unai Emery beat Mauricio Pochettino to the signature of Saliba, one of the most highly-rated young defenders in Europe.
But the clause which kept the teenager in France for this season was considered non-negotiable.
Arsenal were still happy to complete his deal and, according to Arseblog, signed-off on the procedure.
While the surgery does not affect Arsenal’s immediate future, it does pose questions for the future.
Arsenal chiefs were counting on Saliba building his experience of senior football in his native country.
That development will be curtailed with the news that he is out until October at the earliest.