The 36-year-old has undergone surgery on his right ankle after being injured in Saturday's 2-0 win over Darmstadt.
The 36-year-old ex-Germany international has undergone surgery on his right ankle after being injured in Saturday's 2-0 win over Darmstadt.
Fritz, a defensive midfielder who made the last of his 22 appearances for Germany in 2008, is out of contract in June and the injury could end his career.
"On the advice of the doctors and in close consultation with our medical department, Clemens decided to undergo surgery," said Bremen's director of sport Frank Baumann on the club website.
"He will no longer be available to us this season."
Bremen are 14th in Germany's top flight, two points from the bottom three, and the 2003/04 German champions have battled relegation in recent seasons.
"We have always emphasised that Clemens can be an important pillar in this team for the coming season and we will be able to talk about it and tackle the topic in peace," added Baumann.
"The most important thing now is that he recovers as quickly as possible."
Fritz has been at Bremen since 2006, making 368 appearances, and was part of the team which won the German Cup in 2009.