As I recall, Petrov did his medial ligaments. He's already had anterior ligament damage repaired surgically ( injury he was coming back from when the Bulgarian manager decided back to back international games would be a good run out -tosser)
His comeback, given his age, has to be in doubt. But that's not necessarily from a physical injury standpoint. Petrov's game is all about pace and to get that back he would need at least 9 months to a year post op. You can't surgiccally repair knee ligaments without compromising muscle and it will waste further during recovery period. He might be jogging now and in 6 to 8 weeks running. Give it until March and, he'll be really building muscle and geting fit. But will he ever properly sprint again? You have to say it's a doubt. He might, but it's a hell of a lot of work and determination he needs now.