An Australian newspaper has reported that Francois Botha failed a dope test before his heavyweight bout with Sonny Bill Williams in Brisbane on Friday.
The Sydney Morning Herald alleges that the South African veteran tested positive for phentermine which is a banned appetite suppressant.
These reports add further doubts on the credibility of the controversial fight which former Kiwi rugby star Williams won on points.
It was Williams' sixth win in six bouts and his fight with the 44-year-old was reduced to 10 rounds from the original 12 - which was only decided on the day of the clash.
Doubts surfaced over the fight's status as a purported World Boxing Association (WBA) international heavyweight title bout after local media reported that no officials from the organisation were present.
And an incensed Botha, who was well on top during the closing rounds, described the late change of bout length as 'match-fixing' and demanded a rematch.