Basketball players dominate the list (40%) followed by American football and football (soccer) players who make up almost 30% of the top earners.
For the first time since 2010, no female athletes made the list, which Forbes dubbed "an all-male affair".
Note: Forbes' earnings include prize money, salaries and bonuses earned between 1 June 2017 and 1 June 2018.
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. After the windfall from boxing Floyd Mayweather, McGregor's promotional stock has surely risen with the UFC and he could have easily surpassed $13 million in salary and endorsements no matter whom he might have fought in Brazil.
Forbes magazine's estimate of the world's top 100 highest-paid athletes in 2018 is quite the boys club.
Mayweather overtook soccer star Cristiano Ronaldo, who held the money crown the previous two years.
"Boxing's biggest night of 2017 helped Mayweather and McGregor earn almost $400m combined", said Kurt Badenhausen, senior editor at Forbes Media.
Players from 11 different sports are featured in the list, and from 22 different countries.
Others on the list are American basketball player LeBron James (6), Tennis star Roger Federer (7), golfer Tiger Woods (16), tennis player Rafael Nadal (20) and golfer Rory McIlroy (26). His estimated earnings, including endorsements, for 2017 were $285 million.
There were four Boston-based athletes on the list, led by Irving at $36.1 million.
Golden State Warriors star Stephen Curry was the only other National Basketball Association player to feature in the top 10, with earnings of $101 million.
Lewis Hamilton came in at number 12 with earnings of US$51m, making him the highest ranking racing driver on the list.