Assistant Denies Telling Police Lindsay Lohan Was Driving

Gavin the assistant is telling friends, cops questioned him at the hospital where Lindsay was being treated post-accident -- but he neither confirmed nor denied whether Lindsay was driving the car.

Gavin's saying cops confronted him, saying they already knew Lindsay was driving because of the seat belt marks on her left shoulder -- indicating she was in the driver's seat -- and Gavin simply replied with a noncommittal "Okay."

Sources close to Gavin tell us, Gavin believes cops ran with his answer as an affirmative response ... and used it to convince the Santa Monica City Attorney to file a misdemeanor charge against Lindsay.