The 31-year-old has not played for Bayern since the penultimate game of last season and has not stepped on a pitch in anger since France's 4-2 defeat to Holland at Euro 2008.

An operation on his Achilles tendon has kept him out since and that could signal the end of his career.

"I came back in pre-season full of desire, but during the preparation, I had a problem with my Achilles tendon," he explained on France's TF1 television.

"I had to have an operation, which means my recovery will be longer than predicted.

"The hardest thing is not knowing when I could play again. My priority is to find out if I can play football again or not.

"If things have not been resolved by May, my retirement will be certain."