Seems Nate Diaz has changed his mind about running it back with Jorge Masvidal -- saying, "F*ck a rematch."

Remember, Diaz lost the first-ever Bad Mother F*cker match at Madison Square Garden on Saturday ... when the doctor stopped the fight after the 3rd round due to bad cuts on Nate's face.

At the time, both Nate and Jorge declared a rematch WOULD happen -- with Nate saying, "I would love to run it back. That's the only thing I want to do."

But, Diaz has had a change of heart ... and posted the update on IG on Wednesday night.

"F*ck a rematch this shit was over before it started. I’m goin on out on tour. Peace out fight game."