The fight is scheduled for August 26 at the T-Mobile Arena in Las Vegas after months of negotiations.
Mayweather, 40, retired from pro boxing in 2015 after defeating Andre Berto, while McGregor (21-3) beat Eddie Alvarez last November.
The fight is expected to be a 12-round boxing match, with 10-ounce gloves.
When Mayweather steps into the ring against the UFC fighter in Las Vegas on August 26, he looks certain to shatter his previous best of 4.6million pay-per-view purchases. We're going to do UFC Embedded like we do for our fights, and a couple of other things.
Mayweather didn't become one of the best boxers in the history of the sport by overlooking opponents and he won't start with McGregor.
Scotland striker Leigh Griffiths 'gutted' after England's last-gasp leveller
The manager told me just before training on Friday. "We got ourselves into decent positions, but could not finish". I've shared the leadership around and that has been important for us as a team.
"I'm a realist", Leonard Ellerbe, chief executive officer for Mayweather Promotions, said during a conference call Wednesday night. We'll just have to wait and see if that's even close to enough to compete with one of the greatest boxers of all-time. Conor McGregor is 27 and he is a southpaw. The two men will meet at the light-middleweight limit of 154 pounds, which bodes well for McGregor, who is now the UFC's 155-pound champion.
"As with every Mayweather and McGregor fight part of the appeal is the spectacle and outsize personalities who are participating in it", Espinoza said.
Rumors and reports of a fight have been floating for nearly a year, with both fighters openly acknowledging a potential bout.
"As we've already seen this evening, Mayweather vs. McGregor has generated buzz that reaches far beyond that of the considerable boxing and MMA audience".
"McGregor has a lot of confidence because of what he's achieved in the UFC but he's not getting in there with a domestic-level fighter, he's getting in there with one of the greatest fighters of all time".
It's being speculated that both men will be paid a staggering $100 million each for the fight to be aired on pay-per-view TV.