Chris Carlson/Associated Press

Floyd Mayweather filed a petition July 5 asking the IRS for a reprieve from unpaid taxes from 2015 until after his fight with Conor McGregor in August.

"Although the taxpayer has substantial assets, those assets are restricted and primarily illiquid," Mayweather's petition stated, per the legal website Law360 (h/t ESPN.com's Darren Rovell). "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."

Mayweather, 40, made $220 million alone from his 2015 fight against Manny Pacquiao. It is unclear how much he owes the IRS in taxes.

The petition asks the government to reduce Mayweather's penalty on the unpaid taxes. Given a 15-month lapse since the 2015 tax due date, Mayweather would owe 7.5 percent in penalties on top of what he was already scheduled to pay, according to Rovell.

Mayweather is expected to bring home a nine-figure payday from his bout with McGregor, which is slated for Aug. 26 in Las Vegas. The fight will end a nearly two-year retirement. Mayweather has not boxed professionally since defeating Andre Berto via unanimous decision in September 2015, which moved him to 49-0 for his career.

Forbes estimated Mayweather's net worth at $340 million in January.