Chelsea midfielder Michael Essien is expected to be sidelined until January after undergoing knee surgery on Monday.The Ghana international, who has a history of knee injuries, ruptured the anterior cruciate ligament and the meniscus in his right knee in pre-season training last week.

The injury is said to have stunned Chelsea officials, who were expecting scans to reveal a simple twisted knee after Essien fell innocuously during a training drill.

Instead, the 28-year-old has had surgery to repair the torn structures and faces up to six months of rehabilitation before he can return to the Blues.

It is Essien’s third serious knee injury in three years. The midfielder missed a large chunk of the 2008/09 campaign due to cruciate ligament damage and was forced out of the 2010 World Cup with a less severe medial ligament injury.

New Chelsea boss Andre Villas-Boas said: “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.”