Martinez was stretchered off in the first half of the 2-0 defeat to Borussia Dortmund in the DFL-Supercup, and he expects that surgery will be needed to repair the problem, with Bayern medics suggesting that he has damaged his anterior cruciate ligament.
"I'm on the bus and just spoke with the doctor. He told me 99% I got my ACL broken," the Spaniard told members of the media. "I rely on the 1% left but I think I'm in a bad way.
"I'm on the bus with a cold machine. It's so hard. If it's an ACL injury, I'll have surgery tomorrow and I'll start my recovery to come back as soon as possible and be a better player. I'll be back."
If the injury is as serious as first feared, Martinez could miss the majority of Bayern's season.