Now, 24-year-old Ali Walsh is just days away from his PFL MMA debut (against Tom Graesser) ... and TMZ Sports talked to him about fighting as The Greatest's grandchild.

"I definitely have pressure. I even had that pressure in football, and that's a completely different sport. I'm also doing MMA which is also a completely different sport from boxing, but it's also a combat sport, so I think there's gonna be a little bit more pressure there."

FYI, Biaggio was a high school football star in Las Vegas, before playing college ball at the University of California before transferring to UNLV.

Ali Walsh understands he's getting additional attention because of his last name ... but he hopes to be able to blaze his own trail.

"At the end of the day I'm just like any other fighter who's fighting to create their own name, create their own legacy. The only difference is my grandfather is really famous, and because of that I've gotten the platform that I've got, but at the end of the day, it's how you perform in the cage."

"I definitely do have that pressure, but I feel like I'm dealing with it pretty well."

The event, the PFL World Championship, is going down at Madison Square Garden in NYC, under the same roof where Ali fought some of his most memorable fights -- including the "Fight of the Century," Muhammad Ali vs. Joe Frazier in 1971.

We also asked Biaggio if fans might see any similarities between him and his grandfather ... something Ali Walsh says both yes and no too.

"When my grandfather boxed, I feel like it wouldn't translate that well over to MMA. He was very heavy on his lead leg, threw the jab out a lot. If I tried that in MMA, I'd just get leg kicked all day. I've tried that and I've gotten leg kicked and even taken down, so it didn't really work."

"His speed is something that I feel like I have to. I feel like his speed is passed down to me. Dealing with the big stage and the lights and all that, I feel like that's transferred down to me and my brother [Nico], and even my aunt Laila [Ali]."