If Dr. Bennet Omalu -- the inspiration for the famous Will Smith "Concussion" movie -- were advising Elijah Moore following his scary head injury on Thursday night ... he says he'd tell the Browns wideout to retire.
"That is my recommendation," the famed neuropathologist tells TMZ Sports.
Moore was hurt in the second quarter of Cleveland's win over the Jets on "Thursday Night Football" -- and the scene was horrifying.
The 23-year-old's face slammed into the turf .