Floyd Mayweather moving over to MMA just got the thumbs-up from Holly Holm -- who says she could see TBE knucklin' up for the UFC ... and goin' after it with all he's got.
"I'm sure he won't mind putting in the work if he decides to do something with MMA," Holm told the guys on "TMZ Live."
If anyone would know, it'd be Holly -- who won 18 TITLE FIGHTS in boxing before she became a UFC superstar.
But HH -- who's fighting Cris Cyborg at UFC 219 -- ain't saying it's gonna be easy ... in fact, she told us one area where Mayweather's REALLY gotta work if he doesn't wanna get wrecked.
FYI, Floyd shot down fighting for the UFC on Wednesday after Dana White said they were in talks ... but, in the same breath, said the door's always open.