Arsenal captain Mikel Arteta will be out for another three months after having an operation on the left ankle that has kept him sidelined since late November.
Arsenal will also be without France international defender Mathieu Debuchy until April following surgery on the shoulder he injured against Stoke City last weekend.
Spanish midfielder Arteta had a bony spur removed, and Arsenal said: "The procedure went well and Mikel will now begin a period of rehabilitation which is expected to last approximately three months."
Manager Arsene Wenger added: "Mikel has had surgery which went well.
"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."
Arteta has not played since being substituted in the 67th minute of Arsenal's 2-0 win over Borussia Dortmund in the Champions League at the Emirates Stadium on November 26.
Wenger added that 29-year-old Debuchy had surgery on his right shoulder following his injury.
"It's very unfortunate for Mathieu, it's unbelievable because he's had two surgeries in the same season," he said.