Bayern's Ribery injures knee

"It's the knee, it will be necessary to have some additional tests to know more, but we suspect a rupture of the cruciate ligament," said Sagnol at Berlin's Olympic Stadium.

The 34-year-old Ribery, who is out of contract next June, was in clear distress after sprinting for the ball in the 62nd minute and had to be helped off.

Sagnol is in temporary charge after Carlo Ancelotti was sacked on Thursday after Bayern's 3-0 drubbing at Paris Saint-Germain.

Bayern went 2-0 up at Berlin's Olympic Stadium with goals by Mats Hummels and Robert Lewandowski before Hertha roared back with goals by Ondrej Duda and Salomon Kalou.

The result left Bayern second in Germany's top flight, but five points from Bundesliga leaders Borussia Dortmund.