Chelsea midfielder Michael Essien could be out for up to six months following surgery on a knee injury he suffered in training last week, the Premier League club announced Monday. The Ghana international had an operation to repair a ruptured anterior cruciate ligament and meniscus following a right knee injury. According to a Chelsea statement, \"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.\" Essien\'s setback is the third serious knee injury of his career and represents a blow to the Blues as they look to regain the English title from Manchester United after finishing a distant second, by nine points, to the champions last season.