The 27-year-old France international suffered a ligament sprain in his left knee during the 1-1 draw at Wolfsburg on Jan. 15, when it was assumed he would be fit to return after two weeks.
However Ribery will not be available until Bayern's league match at Mainz on Feb. 19 at the earliest, Bild, Germany's biggest selling newspaper, said Thursday.
Ribery was unable to take part in training this week, and a date for his return has not been set by the club.
"It doesn't make any sense to announce a date," coach Luis van Gaal said.
Earlier this season, Ribery missed two months after damaging ankle ligaments in a Bundesliga game against Hoffenheim.