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, ".