Shawn Porter, 'I Won't Fight Claressa Shields'

Boxing sensation Claressa Shields will have to find another male challenger to fight -- because Shawn Porter says he's NOT down to get in the ring with the female superstar.

Porter appeared on the "TMZ Sports" TV show after Shields told us this week she's 100% confident she could BEAT top male fighters like Porter, Keith Thurman and Gennady Golovkin.

So, we asked Porter for his reaction -- to which he smiled and replied, "It's cute!"

Make no mistake -- Porter says he has nothing but respect for Shields as a fighter, but claims boxing a top male fighter is simply "an animal that she's not really prepared for."

Porter says Shields would obviously be outmatched when it comes to strength and power -- but also explains that speed and movement in men's boxing is on a different level than what she's faced in the women's division.

When asked if he'd be down for a 3-round exhibition with Shields to let their fists do the talking -- Porter shot that down ... telling us he's just not interested.

In the full interview, Porter says if Shields is serious about fighting men she needs to start at the bottom and work her way up the rankings ladder like everyone else -- she just can't skip the line and fight a champ.

In the meantime, Shields is working on setting up a fight with the only other reigning undisputed female boxing champ, Cecilia Braekhus.