Arsenal expect to be without Santi Cazorla for three more months after deciding the midfielder needs ankle surgery.
The 31-year-old Spaniard has not featured for the Gunners since the 6-0 Champions League win over Ludogorets on October 19.
It had been hoped the playmaker, who scored twice during Arsenal's impressive opening to the new campaign, would be able to recover without going under the knife.
However, the club announced in a statement that he would need to undergo an operation. "Santi Cazorla is travelling to Sweden early next week to undergo surgery to his right ankle," a statement on www.arsenal.com said.
"The club's medical team and specialists have decided that surgery is required to the plantaris tendon in the Spain international's right foot.
"The problem has not progressed during a rehabilitation programme following the injury during the home match with Ludogorets on October 19.
"We expect Santi's full recovery to take approximately three months.
"Everyone at the club will be working hard with Santi to make sure he's back on the pitch as soon as possible."
Arsenal were beaten 2-0 at home by Southampton in their League Cup quarter-final on Wednesday night.
The Gunners currently sit fourth in the Premier League table, three points behind leaders Chelsea ahead of tomorrow's trip to West Ham.
Meanwhile, Rob Holding believes Arsenal's much-changed side was good enough to win the League Cup despite seeing them crash out against Southampton.
Wenger defended his decision, saying the changes were not the "problem", and defender Holding - one of those drafted into the rotated side - echoed the views of his boss.
"You look at the players we had out, there were some big players," he said.
"You think with the strength of the squad, a second string team can get all the way - but it wasn't to be. It was a chance to get some silverware at the end of the season, so I'm disappointed to be out of the competition.
"There's not much more I can say really. We've just got to learn from it and it'll only help us in the coming years."
The Emirates Stadium was practically half-empty by the time the full-time whistle was blown, and it was greeted by a chorus of jeers from frustrated Arsenal fans as they succumbed to their first defeat since the opening weekend of the season.