A pro MMA fighter nearly had his leg cut off his body in a gruesome car accident last year ... and now he's suing the California Department of Transportation, claiming it's responsible for his tragic injuries.
It's all in court docs obtained by TMZ Sports ... Chris Bonilla -- a former Muay Thai champ who also fought with the Glory kickboxing promotion -- says he crashed into an unmarked barrier on the side of a freeway last year.
Bonilla -- 31 years old at the time -- claims he was driving on the 10 Freeway in West Covina at around 6 AM when he needed to pull off to the side of the road for an unspecified reason.