Watch: Mayweather Sr. rips Justin Bieber over 'Money Fight' take

Justin Bieber is a longtime supporter of Floyd Mayweather, but when asked Tuesday by TMZ Sports if he expects the 40-year-old boxer to knock out Conor McGregor, he replied, "I don't think so."

Those comments didn't sit well with Floyd Mayweather Sr.

"He don't even know boxing," the elder Mayweather told TMZ Sports, adding that Bieber "don't know Floyd like I know him."

Mayweather has walked to the ring with Bieber several times before, though it doesn't sound like the pop star will be in his entourage for the McGregor fight. During an appearance on "Jimmy Kimmel Live!" on Tuesday, Mayweather said Bieber is "going through a lot right now."