Roy Jones Jr., listen up ... here's some sage boxing advice from Rocky himself -- DON'T GET HIT BY MIKE TYSON!!!!
TMZ Sports got Sylvester Stallone leaving Fia in Santa Monica this week ... and when we asked about RJJ's chances in his November exhibition with Iron Mike -- Sly didn't love them.
In fact, Stallone seemed straight-up concerned for Roy!!!
"Well, let's put it this way," Stallone said. "What do you think is going to work? A 22 against a 45???"
Sly added, "Roy Jones is a great, great fighter, but it's just a matter of physics."
Stallone says his advice for Roy when it comes to hanging with Mike in the ring is simple ... "Keep moving!"
"You're talking about, I mean -- everyone knows it. Mike Tyson is a wrecking ball."
The fight is scheduled for Nov. 28 ... and, if you're listening to Sly, that means there's still plenty of time for Roy to not go through with this!!
By the way, when it comes to the rumored Logan Paul vs. Floyd Mayweather fight ... Stallone says he loves LP's guts -- but he clearly doesn't think that scrap should happen either.