"It is just frustrating," he told Bild newspaper on Friday. "I feel basically fit but have been out for three weeks,
"I want to play, help the team but I don't know when I can play again. I have to be patient."
The Dutch winger has played three league matches so far this season.
Bayern, who travel to Fortuna Duesseldorf on Saturday (1330), have not been affected by Robben's absence, winning seven out of seven league matches to top the table on 21 points.