"After I go out there and beat his ass and ragdoll him, that sh*t is coming home with me so I can throw it in my closet."

Of course, Kamaru is the UFC's reigning welterweight champ -- and he was originally set to defend that belt against Gilbert Burns in the first main event on Fight Island.

But, when Gilbert tested positive for COVID and pulled out the fight over the weekend -- Masvidal stepped in and took his place.

Now, Kamaru says he's ready to rock ... and considers his new opponent nothing more than a "minor change."

"At the end of the day, when you’re in training camp, the way that I train, you see no face," Usman tells TMZ Sports.

"When I cross into that Octagon, I have to turn on the Nigerian nightmare and leave Kamaru Usman on the outside. And, so I see no face by the time I'm in there anyway."

"Now it's a little extra push to get in there and really do some damage."

Usman says he's the champ for a reason -- and Masvidal will learn the hard way that he's "definitely not Ben Askren."

Remember, Jorge's stock exploded when he slept Askren with a flying knee in the opening seconds of their fight at UFC 239.

Usman says Masvidal won't pull that crap on him.

"I'm smarter than doing something that silly and being put in that situation. So, I'm definitely not Ben Askren and he's definitely going to have to figure that out the hard way."

There's more ... Usman also told us why he thinks the Masvidal fight came together so quickly (in just a matter of hours).