VfB Stuttgart striker Cacau has been ruled out for at least three months after tearing ligaments in training, the club said.
"I am sad to have been injured that badly in training and in such an innocuous situation and to be missing in these difficult weeks ahead," said the 31-year-old, who earlier this year lost his spot on the Germany squad.
"It is just frustrating," said the Dutch winger, who has played three league matches so far.
"I feel basically fit but have been out for three weeks," he told Bild newspaper on Friday. "I want to play, help the team but I don't know when I can play again. I have to be patient."
Bayern, who travel to Fortuna Dusseldorf on Saturday, have not been affected by Robben's absence, winning seven out of seven league matches to top the table on 21 points.
"If Julian does not have problems with it then he could be in the squad," said Stevens.
