UFC light heavyweight Stephan Bonnar will be sidelined for at least six months after tearing ligaments in his left knee during training on Tuesday in Las Vegas.

Bonnar said he was working on his jiu-jitsu in preparation for his April 2 light heavyweight bout against Matt Hamill in Denver. He said he heard a pop and later learned that he had torn the lateral collateral ligament.

"I was doing nothing out of the ordinary, just working on my (jiu-jitsu) getting ready for my fight," a downcast Bonnar said. "I heard a pop and I thought, 'Damn, what is this?' I walked around on it a little, but when I got home, it was really stiff and swollen."

Though it was initially diagnosed as a partial tear, an MRI revealed a complete tear. He'll have surgery soon in Los Angeles. A ligament from a cadaver will be placed into his knee.

Bonnar, who became one of the UFC's most popular fighters after his rousing fight with Forrest Griffin in the finale of The Ultimate Fighter 1, hasn't fought since submitting Eric Schafer at UFC 77 on Oct. 20 in Cincinnati.

Given the six-month recovery period, it will turn out to be close to a year between fights for Bonnar, who is 11-4.

"What really sucks is that if you break your leg, it feels really bad, but you get on crutches and you sit out six weeks and then you're back and you're good to go," Bonnar said. "In this case, there isn't the pain like a broken leg, but I'm out six months instead of six weeks."