Mike Tolbert only needed to see 17 seconds of Greg Hardy in an Octagon to make a HUGE prediction about his ex-NFL teammate ... telling TMZ Sports, "I could see him being the heavyweight champ of the UFC one day!"
The ex-Panthers fullback -- who was with Hardy for three seasons in Carolina -- tells us he was so impressed with Greg after his fight Tuesday ... he sees a belt in Hardy's future.
"I think if he stays true to it and puts all of his effort into it and continues training," Tolbert says, "... I think he'll be one of the top names in the UFC the next few years."
It's a big statement from Mike ... considering Greg's two fights in a UFC Octagon only total 74 seconds -- but Tolbert knows firsthand what Greg's capable of achieving.
"One of the most athletic people I've ever played with," Mike says.
Mike's also proud of the way Greg's turned his life around after domestic violence allegations and substance abuse issues ... telling us, "I'm so happy for him that he can better himself."