Floyd Mayweather says he can't pay off his 2015 tax liability until after he gets money from his Aug. 26 fight against Conor McGregor.

The boxer filed a Tax Court petition on July 5 that asks the IRS to allow him a reprieve until the fight.

"Although the taxpayer has substantial assets, those assets are restricted and primarily illiquid," the petition said, according to the legal website Law360. "The taxpayer has a significant liquidity event scheduled in about 60 days from which he intends to pay the balance of the 2015 tax liability due and outstanding."

It is not known how much money Mayweather owes, but the IRS had previously argued that Mayweather had the resources to pay it immediately, even if it meant selling property or taking out a loan, Law360 reported.

Mayweather made about $220 million from his fight with Manny Pacquiao on May 2, 2015. Mayweather shared on social media a photo of a $100 million check -- his guaranteed purse from the fight -- which did not have taxes deducted from it. Sources confirmed at the time that the check was genuine.

Mayweather is expected to make a similar amount for the McGregor fight.

On Monday night, Mayweather posted to Instagram, saying he paid $26 million in taxes in 2015 and asking "What else could they possibly want?"

The petition also asks to reduce the penalty Mayweather received from not paying all of his taxes for the year.

The failure-to-pay penalty is typically 0.5 percent of the owed taxes for each month, according to the IRS website. Mayweather's 2015 taxes are currently 15 months past due, which would equal a 7.5 percent charge on top of what is owed.

Mayweather, 40, has earned approximately $700 million in his 49-fight professional career, according to a Forbes magazine estimate.

In an interview with ESPN's Stephen A. Smith in 2015, Mayweather showed Smith his Las Vegas home garage with seven cars that he said were worth "close to $15 million." Mayweather told Smith that he owned the cars but did not drive them.