Floyd Mayweather has asked US authorities for more time to pay his 2015 tax bill, the year of his money-spinning mega-fight with Manny Pacquiao, filings showed Monday.

Mayweather, who is coming out of retirement to fight UFC star Conor McGregor next month, has requested he be allowed to settle his 2015 taxes after he is paid for his August 26 bout.

The McGregor fight is expected to net Mayweather a nine-figure payday, boosting career earnings that have already topped $700 million according to one estimate in Forbes magazine.

Although the 40-year-old pocketed a mammoth $220 million for his May 2015 bout with Pacquiao, a filing to the Internal Revenue Service posted by the Law360.com said Mayweather's assets were mostly "illiquid".

"Although the taxpayer has substantial assets, those assets are restricted and primarily illiquid," the petition said.

Cash flow would improve after the McGregor bout.

"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," the filing added.

Mayweather quit boxing after beating Andre Berto in September 2015.

However he was lured out of retirement to face UFC star McGregor, who has never boxed professionally. The match-up, which has been widely ridiculed, is expected to be one of the most lucrative bouts in history.

Source: AFP