The ex-Germany skipper picked up the injury in training on Tuesday morning and Ribery has stressed that the Bundesliga champions have lost a key player.
"It really hurt to see Philipp lie there on the pitch and I'm really sad for him. All his team-mates and everybody at Bayern really feels for him," Ribery was quoted as saying by Bild.
"We are losing a very important player. He has been a great captain. He was always in great shape and always played well.
"His presence in the dressing room and on the pitch is very important to the team and we will really miss that now. We lose a key player.
"He has to stay calm and focused, even if that isn't easy. He needs the support from his family and his team-mates. We are his family, too, and will do anything to help him."
Lahm has made 18 appearances in all competitions for Bayern so far in 2014-15.