Khoder Nasser, manager of rugby star and heavyweight boxer Sonny Bill Williams, has responded to allegations by Francois Botha that his urine sample was potentially tampered with by a relative of Nasser.

Following a controversial match between Williams and Botha, allegations emerged that a pre-fight drug test taken by Botha tested positive for a banned substance.

Tonight, in an interview with Campbell Live from South Africa, Botha said on the positive results and his previous drug use:

"The thing that bothers me about this whole thing is that Khoda Nasser’s brother or family member was the person who administered the drug test. He took my sample.

“It’s crazy, I paid the price when I was much younger, it cost me millions of dollars – why would I go and do this crazy stuff?”

Nasser responded to these allegations:

“The pathology company is a very reputable pathology company in Australia and Francois has a history with these things and a history with twisting and turning words and scenarios around. He's doing a great job.”