Conor McGregor will get killed if he decided to continue boxing, after a "pathetic" display against Floyd Mayweather Jr.

That's the warning from Floyd Mayweather Sr when asked about the megafight between his son and the MMA star in Las Vegas over the weekend.

Mayweather Sr snapped a parting jab at McGregor, who lost by stoppage in the 10th round of the historic bout at the T-Mobile Arena in Las Vegas on Sunday - after weeks of verbal sparring between the pair.

"No," Mayweather Sr told MMAFighting.com when asked if he was impressed by the 29-year-old Irishman's boxing skills.

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"I don't see nobody even talking the way he talk. Then to go out there and fight like that? Man, that was pathetic, I thought."

Mayweather Sr was particularly displeased by what he called "illegal punches" thrown by the reigning UFC lightweight champion, who had never boxed professionally before luring the 49-0 Mayweather out of retirement with the richest fight in history.

"All the illegal punches and stuff he did. . . you know, hitting in the back of the head. [McGregor] showed me no boxing."

McGregor, who bagged a reported $100 million from the fight, would put himself in danger if he decided to pursue a career in the ring, the 64-year-old Mayweather Sr told the website.

"If he keep [boxing] . . . somebody gonna kill him," he said.

"It all could be about the money with him, because he can't be about no glory ... because what he did was a failure."

And he doesn't want to see his son putting on the gloves again either, despite surpassing Rocky Marciano's record winning streak.

"No, man," Mayweather Sr said when asked if he would support his son coming out of retirement if another big payday presented itself.

"I would definitely have something to say about it.

"If he has another one, I don't think I'd be there."