The Riverside Press Enterprise says ( http://bit.ly/11JlC3f) the man struck his head on the pavement in the fall Sunday night in Moreno Valley, which is in Riverside County.
Sheriff's officials say the white Nissan Maxima was moving slowly when the man fell off.
Paramedics treated the man at the scene and he was taken to a hospital, where he was in critical condition.
Authorities say the car's driver wasn't injured and alcohol was not involved.
Information from: The Press-Enterprise, http://www.pe.com