That's UFC star Gilbert Burns -- who was pulled from UFC 251 for testing positive for coronavirus -- saying he's still down to scrap with Nate Diaz, even while being ravaged by COVID!!!

Yeah, this is some gangster stuff!

Long story short ... Burns was supposed to fight Kamaru Usman in the main event at Fight Island on Saturday -- but COVID killed those plans.

Instead, Jorge Masvidal is taking his place -- and Gilbert says he's super bummed out because he was REALLY looking forward to his title shot.

Still, Burns says he has faith that God has a plan for him -- "My time is gonna come."

In the meantime, Nate Diaz has talked some trash about Burns -- claiming his scrap with Usman wouldn't have been a "real fight."

"This guy is a clown," Burns says ... "I'm as real as it gets."

"If it wasn't for COVID-19, [Usman] would be my 3rd fight in 5 months. And, all tough fights, Demian Maia, Tyron Woodley and Kamaru Usman, the reigning champion."

"And, this guy [Diaz] comes from a loss that he gets beat up from Masvidal."

Burns says simply, "He's just talkin' sh*t ... he don't want no smoke from me."

So, what's next for Gilbert -- he hopes to fight the winner of Usman vs. Masvidal ... but if that doesn't work out, "I would love to beat the sh*t out of Nate Diaz."

As for Gilbert's COVID battle, he's feeling better but he's not out of the woods yet.