Usain Bolt isn't mincing words, flat-out telling TMZ Sports that Tyreek Hill can NOT beat him in a race ... and he's fully willing to prove it on the track!!

And, he'll even risk one of his 8 Olympic gold medals.

We spoke to the 35-year-old track legend -- the fastest man EVER -- about his (good-natured) beef with the 27-year-old KC Chiefs superstar ... and straight-up asked Bolt how the race would go.

"For me I still think I would get him in 40 [yard dash]" ... adding, just to be safe, he'd like the race to be a bit longer -- something like 70 yards.

Somewhat surprisingly, Usain -- who retired in 2017 -- says he'd have to ramp up his training before racing Hill.