Floyd Mayweather

A notice of a federal tax lien filed against the undefeated fighter nicknamed "Money" shows the balance as unpaid as of March 6.

The document was filed with county officials in Las Vegas in April.

Mayweather's tax troubles come as he gets ready to come out of retirement to fight against Irish MMA star Conor McGregor in August.

The lien for 2015 is just the latest in a series of tax liens filed by the IRS against Mayweather over the past decade.

Mayweather's tax lawyer did not immediately return a request seeking comment on Tuesday.

That deal could bring another $100million dollars to his name, more than enough money to make any of his wildest dreams come true - including, perhaps, buying an NBA team. 

Mayweather met with Los Angeles Lakers great and current president of basketball operations Magic Johnson on Thursday in LA and the two apparently talked about NBA ownership.

"It's about time for me to buy an NBA team, if you're ready to sell your NBA team, please get in touch with me," Mayweather wrote on Twitter.

Speculation that UFC star McGregor and retired five-weight world champion Mayweather could meet under Queensbury rules has been growing on a daily basis.

Mayweather, who is arguably the greatest boxer of his generation, wants to unretire to take on McGregor, who is the first man in history to hold two UFC titles simultaneously.

Speculation regarding the potential superfight has been building steam for months but the situation is complicated by McGregor's contract with the UFC, who would have to sign off on any deal.

Mayweather urged MMA star McGregor to stop "crying" about money and sign terms with his UFC bosses, so the pair can meet in a cross-codes fight this summer.

The five-weight world champion told fans he was tired of hearing excuses from McGregor when he appeared at Liverpool's Auditorium on his latest leg of his UK Undefeated Tour on Friday night.

"When I faced Arturo Gatti, I went to his turf and he was the A-side I was the B-side," said Mayweather. "I beat him and I didn't cry or I didn't complain.

Writing on Instagram, Soulja Boy said: "It's going down! Signed my contract I'm leaving the fight with $1,000,000."

According to the rapper the bout will take place in March in Las Vegas and in his corner will be one of the sports all-time greats.

"I got the best ever my big bro @floydmayweather training me damn," he added.

Responding to the announcement Chris Brown told his 34 million Instagram followers it was time to stop talking.

"Now that we have your undivided attention, boxing match set," the singer wrote.

The Digicel SportsMax Fight Night is being dubbed ‘The Final Showdown’, with the pound-for-pound king Floyd ‘Money’ Mayweather declaring that the fight will be his last.

Mayweather (48-0, 26 KOs) will face Andre Berto (30-3, 23 KOs) to defend his undefeated record and WBA & WBC welterweight titles.