According to the 2017 top earning list of Australian athletes, former world number one golfer Jason Day would be the closest to cracking the list, having earned AU$18.9m previous year.
Mayweather, Ronaldo and Tiger Woods are the only three athletes to have topped the list over the past 18 years, Forbes said.
Forbes's sporting rich list is created after calculating an athlete's earnings from prize money, salaries and bonuses in the year to 1 June 2018. McGregor ($99m) sits fourth in the list, with footballers Lionel Messi ($111m) and Cristiano Ronaldo ($108m) second and third.
However, the victor of 23 single grand slam titles has only just returned to action after giving birth to her daughter Alexis nine months ago and, while her endorsements stood at $18 million, it was not enough to remain in the list. Mayweather easily won that bout, but McGregor has the solace of ranking number four on the Forbes list, with estimated earnings of $99 million.
Conor McGregor made a lot of money in 2017 and that earned him top five status among the highest paid athletes in the world.More news: Nabil Fekir's agent breaks silence on reported imminent move to Liverpool
Unsurprisingly, the National Basketball Association dominates the list, with 40 players, 19 of whom are in the top 50 as opposed to the NFL's nine.
Boxing champ Floyd Mayweather and football legend Lionel Messi head the charts in the list of the world's highest-paid athletes according to Forbes.
While McGregor came in at No. 4, his opponent, Floyd Mayweather, ended up at No. 1 overall with reported earnings at $285 million.
The top 100 has an global flavour with athletes from 22 countries, but Americans dominate the action with 66 making the cut thanks to sky-high salaries in baseball, basketball and football.
NBA star LeBron James is the highest-paid basketball player to feature on the list, coming in at sixth rank with total earnings of $112 million, just ahead of Roger Federer, who earned $102 million.
The top 100 athletes earned a total of $3.8bn, up 23% from a year ago.