The California State Athletic Commission had confirmed a license was issued to McGregor.
ESPN and MMAjunkie.com reported that the California State Athletic Commission had confirmed a license was issued to McGregor.
Ireland's McGregor became the first man to simultaneously hold Ultimate Fighting Championship titles in two weight divisions when he beat Eddie Alvarez in New York on November 12.
A powerful puncher, McGregor has previously toyed with the idea of moving from the UFC octagon to the traditional boxing ring -- even floating the idea of taking on undefeated and now-retired Mayweather.
British tabloid the Sun reported in May that McGregor and Mayweather were "on the verge" of agreeing to fight.
Mayweather didn't shoot down the prospect at the time, but Leonard Ellerbe, chief executive of Mayweather Promotions, told ESPN on Wednesday that he didn't see the match-up happening.
"It's all a game," Ellerbe told ESPN. "It's all a calculated effort to gain more fans.
"Conor McGregor can say anything he wants to, but he has a boss and his name is (UFC president) Dana White."
McGregor has been at odds with White before, and after his win over Alvarez said he wanted an equity stake in UFC, which was bought by sports marketing agency WME-IMG in July.