Boxing Star Frank Martin Embracing Underdog Role In Gervonta Fight, 'Fuel To Me'

Frank Martin's hoping more people keep doubting him ahead of his fight against Gervonta "Tank" Davis ... telling TMZ Sports he uses the criticism as "fuel" -- and can't wait to shock the world!!

The WBA Lightweight World Title fight is slated for June 15 at the MGM Grand in Las Vegas ... and Martin (18-0 w/ 12 KOs) says he feels confident to get in the ring with one of the best pound-for-pound boxers in the world.

"I got a lot of things that him, the world, a lot of people may not expect that I got," Martin told us this week.

While some people are skeptical of his chances, Martin isn't losing any sleep over it.

"That s*** embraced," Martin said, "Bet with me, win with me. That s*** is one of them things I embrace. I'm eating off it. It's fuel to me, so it is what it is."

"It ain't gon' change. I just gotta go out there and do the unexpected."

Just because Martin is not the betting favorite (Davis' around -600) in this fight doesn't mean he expects Tank to be relaxed in the ring ... he actually believes the "balanced" and "well-rounded" fighter will be on his A-game.

That's what he's hoping for -- and he sends a direct message to Tank.