White said that McGregor has agreed to step in the ring with the undefeated Mayweather despite not having fought competitively in a boxing ring since he was a teenager. McGregor was granted a license to box in California several months ago.
McGregor, a 28-year-old Irishman, has been the UFC's most popular fighter and among its top money spinners while Mayweather, a 40-year-old American, retired in 2015 with a 49-0 record including 26 victories by knockout.
White has said the fight could generate a payday of $100 million for Mayweather and $75 million for McGregor. Mayweather has repeatedly said that he won't come out of retirement, against anyone, for less than $100 million.
Not everyone would be excited to see a Mayweather-McGregor boxing match.
Promoter Oscar De La Hoya has said a bout between the two would be an "embarrassment" for the sport of boxing.