Floyd Mayweather Sr., father and head trainer of five division world champion Floyd Mayweather Jr. (50-0, 27 KOs), agrees with his son - UFC superstar Conor McGregor should stay far away from boxing.

This past Saturday night, McGregor - the most popular fighter in mixed martial arts - made his professional boxing debut at the T-Mobile Arena in Las Vegas.

He stepped in the ring with Mayweather, who at 40-years-old was coming back from a two year retirement.

McGregor had promised to knock Mayweather out in four rounds - and even predicted a first round knockout after the Nevada State Athletic Commission approved the use of 8-ounce gloves for the bout.

That didn't happen. McGregor started strong, began to fade in the second half and was stopped in the tenth round.

After the fight, McGregor expressed heavy interest in continuing his boxing career.

However, Mayweather advised McGregor to return to the UFC - to avoid getting hurt by a younger, more active boxer.

Mayweather Sr. is in full agreement.

“I haven’t ever seen somebody talking like the way he talk. And then to go out there and fight like that? That was pathetic I thought. Specifically because of all the illegal punches he did, hitting someone in the back of the head. All that kind of stuff, it’s crazy man. He ain’t showing me no boxing. I ain’t seen nothing. Rabbit punches I see. I told my son in the corner... I said ‘When he gets tired, he’s gonna get real tired.’ And he did,” Mayweather Sr. said.

“All the good was about the money for him. Because it can’t be about no glory in what he did, because what he did was a failure. Let me tell you something. If he keeps fighting, doing that thing right there with that boxing right there - somebody gonna kill him.”