TMZ asked the actor, who also appears on Gotham, if he agreed with Mayweather's stance.
"Why does anyone go to an athlete for life advice?" Monaghan said. "He's a great boxer, but he can't read! Don't listen to that guy, it's ridiculous."
Mayweather recently signed off on Trump's "grab her by the p----" tape, which was released by The Washington Post in October 2016, and said it was how "real men" talk.
"Real men speak like, 'Man, she had a fat a--. You see her a--? I had to squeeze her a--. I had to grab that fat a--.' Right?" Mayweather said, "So he talking locker room talk."
To the "real man" sentiment, Monaghan completely disagreed and told the boxer to "be a person" and "be a man."
Mayweather has yet to respond to the actor's remarks.
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