The list is calculated by adding together salaries, bonuses and endorsements, which include sponsorships and appearance fees.
McGregor was stopped in the 10th round in Las Vegas, but was guaranteed to benefit from the record-breaking hype that generated up to £500m.
Ronaldo topped the list this year with earning of £71m, but the Real Madrid star will drop down after McGregor career-high pay day.
“You [Ronaldo] were number one on the Forbes list, I was like number 35 or something,” McGregor said in a meeting last year.
“I’ll get up. Maybe next year I’ll get you.”
Ronaldo had replied: “I don’t think so”.
Despite overtaking Ronaldo, McGregor will not become number one, with Mayweather’s £233m purse putting him back atop of sport’s money-makers.