So, it came as a bit of a surprise when Bieber endorsed Conor McGregor in the big fight taking place in late August, telling TMZ that he didn't think his buddy Mayweather would be able to knock him out.
When asked about Bieber's comments, the father of Floyd Mayweather was well aware of Bieber's slight. And he was harsh in his response. Bieber, who has seemingly always stood up for Mayweather, didn't get the same respect in return.
"Justin Bieber, you understand what I mean, he don't even know boxing," Mayweather Sr. told TMZ.
In a 2015 interview with Complex magazine, Bieber said that Mayweather's critics were stupid.
"With Floyd, he's just an image," Bieber said at the time. "I think he may not do the best job at being humble, but that's not his job. I mean, it's good to see people that are just humble and cool and down-to-earth and chill, but he's trying to get pay-per-view numbers. He's saying wild stuff just for attention. When people can just stop being stupid – sorry to say that – but when people can stop reading into it so much and just look at the fact that he's doing this for entertainment…"
It's unclear if the Bieber and Mayweather have had any sort of falling out, or if Mayweather Sr.'s comments irked the pop star. But Bieber did say he thought it would be a good fight. He just wouldn't back his 40-year-old friend as the sure-fire winner.