Conor McGregor was reportedly ‘knocked out’ during a sparring session in the build-up to his fight with Floyd Mayweather as both fighters publicly defended the validity of the event.

McGregor – the biggest name in mixed martial arts (MMA) – will switch sports to box Mayweather next month, with the American having never lost a fight during his 21 year career.

But while the PR circus continues to ramp up interest in the event, former two-weight boxing champion Jessie Vargas has claimed that McGregor, 29, was knocked out during sparring by fellow UFC star Bradley Wheeler.

In an interview with Villainfy Media, Vargas said: “I heard that they tried Bradley Wheeler but he knocked him out.”

He added: “I’m looking forward to Floyd coming out with a victory by knockout in six, seven rounds. I have no doubt. I actually wanna (sic) put some money on it. It’s a 99 per cent win.”

The claim comes while both fighters have publicly defended the validity of the fight.

“The fans demanded this fight. Conor wanted this. I wanted it, too,” Mayweather, 40, told Talksport. “Those are three things that made it happen.

“Conor is making a lot of money and so am I. The fans want to see this. Conor has the chance to do something no fighter has done before [knock me out].”

McGregor, insisting that “people can say what they want”, said expects to come out unscathed from the bout.

“I believe I will come out of this without a scratch. I will not be nervous. I am a confident young man.”

The fight, which is believed to be worth a whopping £1billion, takes place in Las Vegas on August 26.