Greg Schiano -- BIGTIME SUPPORT FROM EX-PLAYER ... 'He's a Great Coach'

Don't count out Greg Schiano ... so says one of his most famous former players who tells TMZ Sports he's a GREAT COACH ... no matter what the Tampa Bay Buccaneers say.

We spoke to Eric LeGrand -- the former Rutgers University football star who suffered serious spinal damage back in 2010, back when Schiano was the head coach for the Scarlet Knights.

LeGrand -- who's still tight with the recently fired Bucs coach -- says Schiano's not the kind of guy who gives up ... telling us, "After taking a year off, he'll get back into football. That's what he does."

Eric continued, "He's a great coach and he's gonna be great on somebody's program."