Conor McGregor believes he could put Floyd Mayweather down with the first big shot he lands and insists the former-five weight world champion won't make it out of round four when they pair meet on August 26.

The third leg of their four-day publicity tour took place in New York on Thursday and saw the animosity ramp up between the pair ahead of the final press conference in London on Friday evening.

McGregor, who has never boxed professionally, is a massive underdog for the Las Vegas superfight but he is confident the shocking knockout power which made him a sensation in the UFC will transfer into the boxing ring.

"I wouldn't be surprised if the first shot cracks off his temple and he goes down. He won't see round five," McGregor said, predicting a similar outcome to when he knocked then UFC pound-for-pound No 1 Jose Aldo out in just 13 seconds.

Mayweather is the most decorated boxer of his generation and can become the first fighter to amass a 50-0 record, eclipsing legendary heavyweight champion Rocky Marciano, with a victory over McGregor.

But the 40-year-old has never been a renowned knockout artist, finishing just 26 of his 49 career opponents.