Undefeated boxing champion Floyd Mayweather Jr. reportedly received an IV one day before his May victory over Manny Pacquiao, raising questions about whether he violated doping rules. 

Mayweather and the United States Anti-Doping Agency (USADA) say the injection of vitamins and minerals was allowed.

"As already confirmed by the USADA statement, I did not commit any violations of the Nevada or USADA drug testing guidelines. I am very proud to be a clean athlete and will continue to champion the cause," he said in a statement.

AFP reports

A report on the SB Nation sports news website said Mayweather had broken World Anti-Doping Agency (WADA) regulations by having an IV infusion at his home in Las Vegas on May 1, the day before the fight.

WADA guidelines say IV infusions are prohibited because they can be used to mask performance-enhancing drugs, increase plasma volume levels and distort the values of an athlete's biological passport.

But a USADA source told AFP that because Mayweather obtained a therapeutic use exemption, no offence had been committed under WADA rules.

Pacquiao also said he was treated unfairly because the Nevada body refused to let him use a USADA-approved painkiller for the fight, when he was carrying a shoulder injury.

In light of the report, Pacquiao is calling for Mayweather to be punished and demanding a rematch. 

On Fox Business Network, Charles Payne raised the issue with Mayweather, who is set to face Andre Berto Saturday night in what he has promised will be his final fight. 

Mayweather said people have been "taking shots" at him for years in an effort to "taint" his legacy. 

"I'm happy with my legacy, what I've done for the sport of boxing. And I still believe in random blood and urine testing, what I'm currently doing now," he said.

Payne noted the seemingly low level of interest for tomorrow's bout against Berto, in which Mayweather is expected to win easily. 

Payne said the undefeated knockout artist Gennady Golovkin, nicknamed "Triple G," would be another mega-fight for Mayweather, asking him why he did not consider taking on the rising star. 

Mayweather pointed out that Golovkin is a 160-pounder and that he fights at 147. Payne said the two could have agreed on a "catch weight" to make the fight happen. 

"I already beat all the top guys in the sport," he answered.

Asked whether this will really be his last fight, Mayweather said he had a "tremendous career" and that he had always planned for fight #49 - the last on his Showtime contract - to be his last one.

Watch the full interview above.