Floyd Mayweather has given Conor McGregor a startling ultimatum following the Irishman's demand of a US$100 million purse for a boxing match between the pair.

Mayweather challenged McGregor and the UFC to close the deal and make the fight happen during a recent appearance on ESPN's First Take.

"Everybody keeps talking about Conor McGregor. He's blowing smoke up everybody's ass. Dana White, the UFC, let's make it happen. Bring him over to the boxing world, and I'll show him what it's like," 40-year-old Mayweather said.

"They know what my number is. My number is a guaranteed $100 million. That was my number.

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"We are willing to give him $15 million and then we can talk about splitting the percentage - the back end - on the pay-per-view. But of course, we're the 'A side.' How can a guy talk about making 20 or 30 million if he has never made 8 or 9 million in a fight," said Mayweather.

McGregor holds the UFC record for the richest disclosed purse when he made $3 million for his UFC 202 victory over Nate Diaz in their August rematch. That record was matched by Ronda Rousey for her loss to Amanda Nunes at UFC 207 in December.

McGregor isn't expected to make an Octagon return until at least May while taking a break for the birth of his first child.

Talks of a Mayweather-McGregor boxing match caught social media attention in 2016, and McGregor took things one step further just before the new year, obtaining a professional boxing license in California.