Arsenal duo Mikel Arteta and Mathieu Debuchy are facing three months on the sidelines after surgery.
Midfielder Arteta has undergone ankle surgery, while defender Debuchy has had an operation on his shoulder.
Spaniard Arteta, 32, who has not played since the 2-0 victory over Borussia Dortmund in the Champions League on November 26, has been suffering inflammation and discomfort due to a bony spur on his left ankle.
As a result it was decided that the Gunners captain should have an operation in order to solve the problem.
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Arteta is now expected to be on the sidelines for around three months before being fit to play again.
Arsenal manager Arsene Wenger told the club’s official website on Thursday: “Mikel has had surgery which went well. I have just seen him, he is back with us at the training ground.
“He had limited mobility in his ankle and some persistent inflammation that had an impact on his calf.
“That meant we had to make the decision to have surgery and it's a proper solution which gives him the best chance to recover.”
Mikel has had surgery which went well.... I count three months out for Mathieu because contact will be a problem for the shoulder.
France international Debuchy only returned from three months out with an ankle injury in December but injured his shoulder when he collided with an advertising hoarding during Sunday's 3-0 win over Stoke.
And Wenger reported: "Mathieu had a surgery on his right shoulder following the injury on Sunday.
"It's very unfortunate for Mathieu. It's unbelievable because he's had two surgeries in the same season. He just came back, he played seven games, and he's out again.
"I count three months out for Mathieu because contact will be a problem for the shoulder."
Wenger had better news regarding another of his full-backs, adding: "Kieran Gibbs will be training again with the squad on Friday and we will see how he goes from there. His news is positive."
However, forward Danny Welbeck is set to miss Sunday's clash with Manchester City due to a thigh injury.
"Danny is not ready yet," said Wenger. "He is still feeling some pain, so we will have to be patient."