Petrov's injury - which occurred on international duty with Bulgaria against Georgia last month - failed to respond to treatment.

The former Atletico Madrid star is scheduled to return to Spain next week for an operation.

City manager Mark Hughes said: "Martin is going to see a surgeon on Monday and he will probably stay and have an operation.

outstanding performers

"If that is the case he will probably be out for three to four months. That would be a blow for us as he gives us more options.

"Unfortunately it is a frustration for us as it happened on international duty. That makes it a bit more difficult to take.

"Martin had a good pre-season and last year he was one of our outstanding performers. But at the moment it looks as though he will have to go in for an operation."