Boxer Francois Botha of South Africa has been accused of failing a drug test before his heavyweight bout against Sonny Bill Williams in Brisbane on Friday.
The Sydney Morning Herald reports Botha, 44, tested positive for phentermine, a banned appetite suppressant, before losing to Williams on points after the bout was reduced from 12 rounds to 10.
The test, which has been forwarded to the World Boxing Association headquarters in Panama, was also said to have detected traces of benzodiazepine, a valium-like product.
Williams defeated Botha in a unanimous points decision.
Bookmakers refunded bets on the win and Botha on Saturday challenged Williams to a rematch.
Williams, who was on the receiving end of some heavy blows from Botha in the final round, tweeted on Saturday that both camps knew it was a 10-round affair.
AAP reports that Botha's management apparently failed to tell him it had been cut to 10 rounds.
Ringside judges gave Williams the victory 97-91, 98-94 and 97-91, which was greeted by considerable booing from the crowd.