Arsenal suffered a sizeable blow on Thursday when influential Spanish midfielder Santi Cazorla was ruled out for around three months due to an ankle injury.
The 31-year-old Spain international has not played since sustaining the injury during Arsenal's 6-0 Champions League win over Bulgarians Ludogorets Razgrad on October 19.
He will undergo surgery in Sweden next week and is not expected to return until the beginning of March, meaning he will miss a crucial chunk of Arsenal's season.
"The club's medical team and specialists have decided that surgery is required to the plantaris tendon in the Spain international's right foot," Arsenal said in a statement on their website.
"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."
Arsenal lost 2-0 at home to Southampton in the League Cup quarter-finals on Wednesday night, but have reached the Champions League last 16.
They currently sit fourth in the Premier League table, three points below leaders Chelsea, ahead of Saturday's trip to London rivals West Ham United.