Franck Ribery was forced out of Bayern Munich's 2-2 draw against Hertha Berlin with a leg injury club sporting director Hasan Salihamidzic says "doesn't look good."
The former France international was examined by Bayern medical staff after leaving the game in visible pain just after the hour mark.
And Salihamidzic told reporters he and the club are hoping for the best, despite discouraging early signs.
"There's the injury to Franck Ribery -- Franck is in real pain," he said. "We hope it isn't too bad but it doesn't look good.
"The doctor is investigating him. He could not examine him at first, because he had so much pain."
ESPN FC's Germany correspondent Mark Lovell contributed to this report.