Floyd Mayweather Jr. celebrates win against Robert Guerrero in Las Vegas. (Ethan Miller/Getty Images Sports)

Boxing champion Floyd Mayweather Jr. was named the highest-paid U.S. athlete for the second year in a row, and Nike does not endorse him; nor does he own a clothing line, ABC reports.

Mayweather, 36, was paid $90 million in the last year, none of it coming from endorsements, according to Sports Illustrated.

"I earn a lot of money but the money is not what motivates me," Mayweather said in a statement. "I work very hard at my craft and appreciate all the fans that support my efforts by buying my fights. Being at the top of my sport for over a decade validates my willingness to train hard, fight hard and give everyone something to enjoy. It is a honor to be the highest paid athlete again this year but it is just a part of my love for the sport of boxing and what it has done for myself and my family."

Coming in second in Sports Illustrated’s list is LeBron James, who is competing in the NBA playoffs with the Miami Heat. He earned $56.5 million in total, $17.5 million of which was his salary and $39 million of which came from endorsements. James has a few basketball shoes named after him included in his deal with Nike plus endorsements from Coca-Cola, McDonald’s and Samsung.

So how is it that Mayweather surpassed James by $33.5 million?

First, Greyser pointed out, compensation for boxers is not particularly high.

"Only the absolute top tier of boxers are able to cash in significantly," he said.

Mayweather clearly fits that bill. He received the highest guaranteed purse in the history of boxing with his last fight at $32 million. He also is his own fight promoter through his own company, Mayweather Promotions. He also has fought successfully in not just one but three weight classes.

Read more at ABC.