The planet's best female boxer tells TMZ Sports she's been in contact with the UFC superstar about some MMA lessons to get ready for a possible tilt with Nunes ... and it looks like those will all go down after Jones' fight with Dominick Reyes in February.

"He said after he fights, I could come down there a week or two and see how I feel doing MMA stuff."

Of course, if Shields had her way ... there would be no need for the workouts -- she wants a fight with Nunes to be strictly boxing only.

But, Amanda told us last month the only way she's getting in the ring with Shields is if it's an MMA fight ... so Claressa is taking the steps to get the ball rolling on that.

Shields says she's actually "excited" AND "scared" to begin learning the tools for the possible bout ... telling us, "I'm going to have to learn so much more stuff and I just hope that I like it."

As for what will happen when she feels her MMA skills are good enough to take on Nunes ... Shields says she expects that fight to be BIGGER than Floyd Mayweather vs. Conor McGregor!!

But before stepping in the cage ... Shields has a big time boxing match this Friday against Ivana Habazin in Atlantic City.