Rapper Bone Crusher -- I Was NOT in Motorized Cart Because I'm Fat, Dammit

Rapper Bone Crusher wasn't rolling around a Minnesota mall in a motorized cart this week because he's fat -- despite reports to the contrary -- he tells TMZ, he's got a REAL reason for being temporarily handicapped.

Mr. Crusher tells us, he recently underwent serious knee surgery to repair an injury he sustained a few years ago in Germany, when he was performing for U.S. troops stationed abroad ... and stupidly jumped off stage.

Crush -- real name Wayne Hardnett, Jr. -- says he's been rehabbing the knee since the surgery and that's why he had to use the motorized cart. The rapper says he can walk just fine, just not for extended periods of time ... yet.

That said, Crusher -- who currently weighs roughly 360 pounds -- admits the photos that surfaced on the web this week weren't so flattering, telling TMZ, "I'm definitely trying to lose weight. I want to get myself back down to where I was on 'Celebrity Fit Club.'"

Crusher says his goal weight is 250, and he's already lost roughly 40 pounds since focusing on his weight again.