British boxer Dillian Whyte insists he won his fight with Oscar Rivas "fair and square" amid allegations of a positive drug test.
A report from BoxingScene claimed Whyte reportedly tested positive for at least two banned substances prior to Sunday's (NZ time) victory over Columbian Rivas at the O2 Arena in London.
Whyte's promoter Eddie Hearn said the 31-year-old heavyweight was cleared to fight after facing an independent panel on the day of the fight.
If proven to be true Whyte faces an eight-year suspension, having served a two-year ban between 2012-14 for unknowingly taking an illegal supplement.
Whyte - who beat Joseph Parker last year - broke his silence, taking to social media to express his feelings.
"I am so disappointed with the rubbish that has been said about me over the last few days," he posted on Twitter.
"I have lawyers dealing with it, and I have been told that I can't talk about it for good legal reasons. I was cleared to fight, and I won that fight fair and square. Thanks for the support."
A report from the BBC said the UK Anti-Doping (Ukad) would be making no comment, while the World Boxing Council (WBC) said it had not received any notification about a positive anti-doping test, adding that it is "reviewing the situation".
The win over Rivas saw Whyte become the mandatory challenger for the World Boxing Council title held by the American Deontay Wilder.
Speaking to UK sports radio station talkSPORT, Wilder said he was disheartened upon hearing about Whyte's failed test.
"I just shook my head. It's over and over again, how many times are we going to hear of fighters doing this?
"We are going to continue to hear about this happening because there are always drugs coming out that can't be detected yet.
"He was so close, he was crying about how he wasn't getting opportunities to be the mandatory, how he had to wait 600 days. He had four opportunities, he just didn't want to take them - he wanted people to feel sorry for him.
"He finally gets his chance, he finally becomes the mandatory and then, damn.
"There have been reports that they knew three days prior to this happening that this was going on and they didn't report it to the WBC or the opponent, and if everything comes back to be positive, they are in for a massive lawsuit.
"The system needs to change. I believe in second chances but I also believe in a system of three strikes, and you're out - banned for life. They have to start laying down the law. Someone has to stop the bleeding somewhere."