Arsenal have confirmed defender Calum Chambers ruptured the anterior cruciate ligament of his left knee in Sunday’s defeat by Chelsea.
Chambers, 24, had successful surgery on Thursday and is expected to be out for action for six to nine months.
The centre-back, who has made 18 appearances in all competitions this season, suffered the injury in the first half at Emirates Stadium.
Gunners boss Mikel Arteta previously said the injury was “significant”.
Meanwhile, Arsenal hope left-back Kieran Tierney will return to training in March after undergoing surgery on the dislocated shoulder he sustained in the 3-1 win over West Ham on 9 December.