Floyd Mayweather Sr. Blasts Justin Bieber: 'He Don't Know Boxing'

You thought things were heated when Floyd Mayweather Jr. and MMA star Conor McGregor faced off last month in a testy press conference to promote their Aug. 26 grudge match? Well, they just got turned up a notch, because Floyd's dad, Floyd Mayweather Sr., now has beef of his own.

According to TMZ, the undefeated, five-division champ's dad is lashing out at Floyd's longtime pal, Justin Bieber, claiming the "Friends" singer doesn't know anything about boxing and should keep his mouth shut. Bieber -- who walked longtime pal Mayweather into the ring for his ultra-hyped 2015 showdown with Manny Pacquiao -- was caught by paparazzi earlier this week on a walk in Los Angeles giving his thoughts on the fight. And while he repped Team Mayweather, Justin gave a firm "I don't think so" when asked if Floyd would knock McGregor out.

I think it'll be a good fight," said Bieber.

Floyd Sr. was not having any of that. "Justin Bieber... he don't even know boxing," Mayweather's dad said. "He knows Floyd, but he doesn't know Floyd like I know him."