Devin Haney Says Jake Paul Shouldn't Box Amanda Nunes, 'Guys Should Fight Guys'

Boxing star Devin Haney does NOT like the idea of Jake Paul fighting UFC champ Amanda Nunes ... telling TMZ Sports it's simple -- "Guys should fight guys."

Remember, UFC honcho Dana White previously told us he might let The Lioness whoop Paul's ass after the social media superstar offered Conor McGregor $50 MILLION to take a fight earlier this week.

Nunes -- the current bantamweight and featherweight champ -- responded to White's comments on Twitter ... saying, "I'm in!"

So, when we spoke with the WBC lightweight champ outside Dior in Beverly Hills ... we had to get his take on the potential battle of the sexes ... and Haney's not with it.

"I don't think he should fight a girl," Haney tells us. "I think he's still a man. He gotta fight a man."

Of course, Nunes is one of the greatest fighters in UFC history ... and Paul only has 2 "pro" fights under his belt against inexperienced opponents.

But, that doesn't mean anything to Haney.

"No, it's not fair. Girls should fight girls. Guys should fight guys."

Despite being new to the sport, Haney praises Paul's work ethic in the gym ... saying he's trained with the guy and knows he's taking it seriously.

"That's my boy, so I like that he's doing good ... I've been in the gym with him. He's showing that he's dedicated to the sport."

So ... what do y'all think??