Martin Gramatica -- one of the greatest Tampa Bay kickers of all time -- is vouching for Nick Folk ... saying his beloved Bucs should NOT fire the guy ... at least not yet. 

Gramatica won a Super Bowl with the Bucs back in 2003 -- and as you can see in the back of the shot, his trophy room is filled with game balls from making clutch kicks. 

So, after Folk crapped the bed on Thursday Night Football -- going 0-3 -- we hit up Martin for his take. 

"I felt horrible for him," Gramatica tells TMZ Sports ... "that feeling that you get, only kickers understand."

But Martin says he knows Folk -- and if you look at his stats, he's a good kicker -- and he hopes the Bucs give him one more shot to prove it before cutting bait.