McGregor, a UFC star, and Mayweather, who retired from boxing in September 2015 after winning all 49 of his pro fights, will box in Las Vegas at the T-Mobile Arena on Aug. 26.
The two colorful fighters swapped obscenities and verbal jabs as they worked to whip up attention for the Aug. 26 pay-per-view broadcast.
McGregor, widely seen as the underdog because his specialty is mixed martial arts, not boxing, made a bold prediction: "I'm gonna knock him out inside four rounds, mark my words"
Mayweather, who is 40, said he's not the same fighter he was years ago but said he would have no problem handling McGregor.
"We know Mr. Tapout like to quit. You will wave that white flag," Mayweather said.
Over the course of his career, Mayweather has generated 20 million views and $1.3 billion in revenue on pay-per-view, according to Showtime Sports head Stephen Espinoza.
At one point, Mayweather bashed McGregor for fighting for such smaller stakes than the more lucrative bouts he and his The Money Team have negotiated. He pulled out a $100 million check from his backpack.
McGregor, though, quickly responded with an allusion to the boxer's IRS troubles: "That's for the tax man."
The location of the fight was moved this week when promoters reached an agreement with Ice Cube to move the championship of his Big3 basketball league from the T-Mobile Arena to the MGM Grand Garden Arena on that same date. The T-Mobile Arena, which opened last year, has a capacity of about 20,000.
Mayweather and McGregor are launching a four-city tour this week to promote the fight.