But the Stockton native has been undergoing a strict new diet and training regimen as he now looks in fantastic shape ahead of his potential return to MMA in 2021.
Covington, 32, bounced back from his UFC 245 defeat to Kamaru Usman last weekend as he picked up a TKO victory over Tyron Woodley.
The outspoken American star said that he was set to fight Diaz at Madison Square Garden in 2018, but he suggested that he didn't "want to mess with me."
Speaking at the UFC Vegas 11 post-fight press conference, Covington explained: "I signed to fight him at Madison Square Garden two years ago and he was going to sign and he backed out last minute.
"That's an easy-money paycheque. [...] I'm a kid from a small town in Oregon living the American dream.
"He doesn't want to mess with me because he knows I'll take his life inside that octagon and he'll never be the same person again."
Covington has been linked with fights against rivals Jorge Masvidal and Usman, but 'Chaos' would welcome a fight with a "high-pressure fighter" like Diaz.
However, the former interim UFC welterweight champ added that the Diaz fight would be "easy" and he would retire him "like I retired Tyron Woodley."
Covington continued: "I would love to fight Nick. He's a high-pressure fighter. I'd love to fight him and it would be an easy fight.
"I'd definitely retire him just like I retired Tyron Woodley. Nick Diaz would never fight again, I promise you, after I got done with him."
UFC president Dana White is far from optimistic about Diaz's potential MMA return by saying he doesn't have any "expectations" and will wait to "see how this thing plays out."
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