NFL's Mike Tolbert Greg Hardy Will Be Heavyweight Champ

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…