The Bundesliga champions' official site said that Sagnol went under the knife at Bogenhausen hospital and that he is 'set for a lengthy spell on the sidelines'.

Sagnol spent most of last season struggling with injuries, which included a slipped disc and a knee problem.

The 31-year-old full-back was part of France's squad in EURO 2008, but announced his international retirement after a dismal campaign in Austria and Switzerland.

Meanwhile, Bayern will face Italian champions Inter Milan on Tuesday, before kicking off their Bundesliga campaign against Hamburg on august 15th.