Or, "you gonna go broke!"

TMZ Sports talked to the 26-year-old, undefeated (14-0, 12 KOs) boxer ahead of his highly anticipated matchup with Tank (26-0, 24 KOs) ... with the WBA lightweight title on the line.

While both men are undefeated, the bout isn't even in oddsmakers' minds

In fact, Davis is around a -1,000 favorite ... meaning you need to risk a grand just to win $100 on Tank.

The inverse of that -- if you bet on Romero and he wins, you're going to make bank. And, that's exactly what Rolly says you should do.

"Go place your bet, make your money. I get rich, y'all get rich," Rolly said.

"The only people that don't get rich are dumbasses who bet on Tank. You bet on Tank, you're gonna go broke."

The 14-0 boxer is so sure of himself he's suggesting folks put everything on the line ... 'cause he's leaving the ring with the WBA belt.

"I'm gonna tell everybody to bet everything they got 'cause the thing is, I'd bet everything I got because that's the thing is, I'd bet everything I got!"

But, don't think the advice is free, 'cause once he wins, Rolly wants something back in return.

"Everyone who bets on me is gonna thank me and honestly I hope everybody buys me a nice dinner after this s**t!"

"I'm gonna win. I'm gonna knock him out!"

As for Tank, (as you'd imagine) he believes the fight will go a little differently ... and he told us as much when we talked to him on Thursday.

"It's gonna take some time to break him down because of his body size but he's definitely getting broke down for sure," Gervonta told us.

"He bruises easily. His face was messed up against someone who can't hit -- imagine me."