TMZ Sports talked to the 27-year-old undefeated fighter days before his huge UFC 273 scrap with 35-year-old Burns, the #2 ranked 170 pounder ... and we asked Borz why Usman was assisting with the training.

"I feel sorry for both those guys. I'm gonna smash the guy and punch his face and his best friend will be standing there in the corner and make him scared as well, ya know," Chimaev told us.

FWIW, Usman isn't cornering Burns. As he usually does, Vicente Luque -- Gilbert's best friend -- will be in his buddy's corner for the fight.

On Friday, we broke the story ... Usman, the top pound-for-pound mixed martial artist in the UFC, is helping Gilbert prepare for Khamzat. It was surprising because the Nigerian Nightmare and Burns had a bit of a falling out before they fought for the title in February 2021 ... a fight Kamaru won by TKO.

We asked the 10-0 fighter why he believed Usman was helping Burns ... and if it indicated Kamaru was rooting for Durinho.

"Of course 'cause he's afraid. They push him down under me, you know, because he's scared, that's why. That's why he wants to stop me before I come for him."

We asked Khamzat, currently ranked 11th in the division, if he believes a win would be enough to set him up for a title shot against Usman, who hasn't lost a fight in nearly a decade (Kamaru's won 19 straight!).

"Of course. The guy number two in the division that's why I smash him, what are they gonna do? After that, they have to fight me."

Even though he's ranked significantly lower than Gilbert (who BTW is one of the BADDEST men in the world), Khamzat is a significant betting favorite in their fight ... with bettors having to lay down over $500 to win $100.

Chimaev -- who has run through his previous 4 UFC opponents (just 1 took him to the 2nd round) -- his fight with Burns stands to be the toughest challenge he's faced in Dana White's organization.

Shockingly, Khamzat has only been hit 4 times in those 4 fights ... an incredible stat, but one with which Chimaev ain't concerned.