Arsenal striker Danny Welbeck is expected to be out until Christmas after having knee surgery.
Welbeck, 24, sustained the injury at the end of April, after scoring eight goals in his first 34 Arsenal games.
“The injury to his cartilage did not respond as well as hoped and the decision was taken last week for him to undergo surgery,” said a statement.
Arsenal were the only club from the top five European leagues not to sign an outfield player during the summer.
That led to the Arsenal Supporters’ Trust calling for an inquiry into the club’s transfer policy.
“No-one wants Arsenal to buy players just for the sake of it, but we do want to see the money being invested to make the club stronger,” it said in a statement.
Goalkeeper Petr Cech was Arsenal’s only transfer-window signing.
Manager Arsene Wenger said: “Am I happy with the investment I make? Yes, every time. You have to find the players to invest in.”