The Irish superstar noted that Tuesday marks the 3-year anniversary of McGregor vs. Diaz II -- a fight Conor won by split decision at UFC 202 in 2016.

"3 years to the day myself and this Mexican animal went to war," Conor said.

Then he dropped this bomb -- "I’ll be prepared for it when we go again. If we go again."

"If not, respect always. A war for the ages. No bitch talk. Just real sh*t."

Conor also congratulated Diaz on his dominant victory over Anthony Pettis at UFC 241 over the weekend ... saying, "It was motivating to see it for my own comeback."

"I don’t blame you not mentioning me for the trilogy bout post fight, you know what I’m like when I get going. Vicious."

Conor hasn't fought since his loss to Khabib Nurmagomedov at UFC 229 in October -- and while Dana White has told us he expects to see Conor back in the Octagon in 2019, he hasn't specified an opponent.

Clearly, Conor has his eyes on Nate ... but Diaz called out Jorge Masvidal instead.