The UFC Hall of Famer was on "TMZ Live" Monday to discuss the bizarre challenge JB's thrown down ... practically begging Tom to get in the Octagon with him for an MMA brawl. Urijah says there's one huge X-factor -- and it's why he gives TC the edge -- Cruise is an experienced wrestler.
That's right, long before he was Jack Reacher and Ethan Hunt ... Tom was throwing it down on the wrestling team at Glen Ridge High School in New Jersey. Check out the vid ... Urijah says he's seen the Biebs throw a punch and long story short ... he ain't impressed.
Whatever the case ... Urijah says he'd promote the hell outta the match if TC ever agrees to the challenge. To be fair, he does say Bieber has one factor on his side.
Urijah also has a very serious question -- one we're ALL thinking: What's JB's beef with Tom???
For the record ... Tom's still not responding to the challenge.