"It would be a hell of a fight," Reigns tells TMZ Sports. "But when it comes to the squared circle, I don't think there's anybody better in the world [than me]. So, yeah, I feel VERY comfortable being in the ring with Jon Jones."

Of course, a WWE scrap between the two massive fight stars is now a possibility because Jones just told Sports Illustrated this week a move to the squared circle at some point is "inevitable."

When we got Reigns out at L.A.'s new Sofi Stadium (the home of WrestleMania 37 in 2021!!), he told us he would LOVE to be a part of a bout with the UFC legend in the future.

"Oh, for sure, man," Roman says. "Someone like Jon Jones, I mean, if you're going to step in the WWE ring, you're most likely going to want to step in there with the big dog."

As for how Jones would fare outside of a match with Reigns ... Roman says he believes Jon's got a chance to be a real superstar in the WWE.

By the way, Reigns also gave some advice to Dwayne Johnson's daughter, Simone Johnson, who's now training to be a WWE Superstar.

Roman tells us he'd like to see her blaze her own trail with the future of her character, as opposed to following in the footsteps of "The Rock" ... saying, "It's better to create your stuff."