Floyd Mayweather has denied he broke any rules by receiving an infusion of saline and vitamins on the eve of his fight with Manny Pacquiao.
A report surfaced claiming that Mayweather was given an IV drip the night before the bout, and that he had received favourable treatment from the US Anti-Doping Agency (Usada), who gave him an exemption.
Usada has denied the report, saying it is "riddled with significant inaccuracies and misrepresentations.
“We believe it is important to immediately correct the false suggestion that Floyd Mayweather violated the rules by receiving an IV infusion of saline and vitamins.
"It is simply absurd to suggest that we would ever compromise our integrity for any sport or athlete."
And Mayweather has now also commented on the report, saying: “I follow and have always followed the rules of Nevada and Usada, the gold standard of drug testing.
“I am very proud to be a clean athlete and will continue to champion the cause.
"Let's not forget that I was the one six years ago who insisted on elevating the level of drug testing for all my fights."
Central to the reports claim of cheating is that an infusion such as the one Mayweather received "can dilute or mask the presence of another substance that is already in the recipient's system".
It claimed that Usada learned of the infusion while visiting Mayweather at his home in Las Vegas on May 1 to conduct an unannounced test.
But Usada said that while Mayweather's application for the infusion was not approved until after the fight, he did disclose it to them prior to it being administered.
"Mr Mayweather's use of the IV was not prohibited under the NSAC rules at that time and would not be a violation of the NSAC rules today," Usada's statement added.