Chelsea have confirmed that Michael Essien's latest knee injury will keep him on the sidelines for up to six months.
The Ghana midfielder damaged ligaments in his right knee during a training session last week, the third serious knee blow of his career, and has undergone an operation.
A club statement read: "Following an injury to his right knee in training last week, Michael Essien had surgery today to repair a ruptured anterior cruciate ligament and meniscus. The surgery was successful and Michael's full recovery could take up to six months."
Chelsea manager Andre Villas-Boas added: "Everyone at Chelsea wishes Michael well for his recovery. His team-mates and all the staff and I look forward to helping him return to playing as soon as possible."
The Blues are now expected to move in the market for a new midfielder, with Joao Moutinho of Porto linked with a reunion with Villas-Boas, and a return of Scott Parker to Stamford Bridge also floated.