"No NHL players or Nascar drivers earned $20 million during the past year", the website said.
That's according to Forbes magazine, which estimated the now-retired pugilist's annual income from June 1, 2017 to June 1, 2018 was at a whopping $285 million - $275 million of which was classified as "salary/winnings".
Serena Williams - victor of 23 grand slam tennis singles titles - was a year ago the sole female representative, but she has since largely been inactive, owing to pregnancy and giving birth to her daughter Alexis in September.
He earned a $275m (£205m) payday for his boxing match in August against UFC star Conor McGregor, who is number four on the United States business magazine's list.
Three mega stars of Formula 1 have unsurprisingly made it to Forbes 2018 Top 100 highest-paid athletes list, and the names are equally predictable.
LeBron James was the highest-ranking basketball player, grabbing sixth place with earnings of US$85.5m.
Is Marouane Fellaini About To Trade Man Utd For Arsenal?
The 30-year-old is believed to be in talks with several clubs already, namely AC Milan , Paris Saint-Germain and West Ham United. Juillard told followers on social media that Fellaini will meet with Arsenal reps "at the beginning of the week".
Lionel Messi and Cristiano Ronaldo both earn around the £80million per year mark, though one star does rank higher than the other.
McGregor meanwhile vaulted up the rankings to fourth spot, thanks to his $112 million cut of the Mayweather purse.
Messi's annual salary, including bonus payments, is said to be $84 million (R1.07 billion) following his latest contract extension, while he also earned an extra $27 million (R343 million) from endorsement deals with the likes of adidas, Gatorade, Pepsi and Huawei to take his overall income to $111 million (R1.41 billion).
In the top 100 list the National Football League had 18 athletes, 14 were baseball players and nine were footballers.
The top 100 earned $3.8 billion, a 23 percent jump over past year. As per the list, the top-100 athletes hail from a total of 22 countries and compete across 11 sporting disciplines.
Elsewhere, Britain's Formula One world champion Lewis Hamilton is the highest paid figure from motorsport to feature, coming in at 12th with $67 million.