Meet Mohammed Usman -- Kamaru's younger brother -- who's set to compete in the PFL's $1 million heavyweight tournament ... and turns out, fighting talent runs in the family.

32-year-old Mohammed is 6'2", 265 pounds -- and previously played defensive end at the University of Arizona.

Now, he's focused on MMA -- he's 7-1 as a pro and currently on a 4-fight win streak.

Usman will step into the cage to fight Brandon Sayles on Thursday -- and hopes to score a win to advance to in the $1 million tourney.

Mohammed says he knows his brother's rise to superstardom makes him more of a target -- but he loves the pressure and can't wait to show the world he's a legit contender.

"I'm at a point in my life and my career that I'm a complete fighter," Usman tells TMZ Sports ... "So, I'm gonna go out and put pressure and everything that I want to happen will happen."

Kamaru -- the UFC's reigning welterweight champ -- also believes his bro is the real deal.

"The thing is Mohammed ... he was just a raw, athletic specimen and I’ve got him to commit to it. He’s really putting in the time and the effort right now."

Mohammed says he's got a friendly competition with his big bro when it comes to knockouts ... and since Kamaru obliterated Jorge Masvidal in the 2nd round of their fight, Mo is gunning for a 1st round KO on Thursday.