Francois Botha (right) had Sonny Bill Williams on the ropes in the 10th round of their controversial fight.

Francois Botha (left) raises his arm anticipating victory, which went to Sonny Bill Williams by unanimous points decision.

Sonny Bill Williams with his entourage which includes Quade Cooper (second left) and Anthony Mundine (third left).

Francois Botha, the former heavyweight world champion beaten by former All Black Sonny Bill Williams on Friday night, has tested positive to a banned substance.

Botha, whose claims that he did not know the WBA international heavyweight bout would only last 10 rounds have also now been discredited, failed a drugs test on the eve of the fight.

Results of a urine sample submitted by the 44-year-old South African in Brisbane last Tuesday under WBA regulations show he had Phentermine - a banned stimulant - in his system.

The drugs test, which has now been forwarded to the WBA's global headquarters in Panama, also detected Benzodiazepine, which suggested Botha was also using a valium-type product.

After the fight, Williams has tried to placate Botha with a rematch in South Africa, although it seems unlikely to be sanctioned by the World Boxing Association.

As condemnation stemming from Friday night's controversial bout at the Brisbane Entertainment Centre continues, Williams confirmed his post-fight offer to resume their unfinished business at the end of his National Rugby League campaign with the Sydney Roosters.

Botha demanded a rematch after their battle for the vacant belt culminated in the 44-year-old claiming he had been robbed of the title because the duration of the contest was surprisingly shortened from the regulation 12 rounds to 10.

Williams won by unanimous points decision but was on the verge of losing his unbeaten professional record - now 6 and 0 - after Botha landed telling blows in the dying seconds.

The former All Black formalised his offer to fight Botha again via his Twitter account yesterday saying: "After, God willing, having a good footy season, I'll gladly rematch Mr Botha. Even in South Africa". In a rare moment of levity after the fight Williams joked he would happily fight in Cape Town because he would boast a bigger fan base than the Afrikaner - a by-product of his rugby-based popularity with the coloured community.

However, should the rematch eventuate there is only expected to be pride on the line as the WBA continue to probe the so-called title fight.

Advised that his organisation's "prestigious" title has been "disgraced" by the dramas that unfolded on Friday night, WBA vice-president Gilberto Mendoza has pledged to investigate.

"Reading all about the controversy," he posted on Twitter.

The Panamanian has already been beaten to the punch by the WBA's Oceania representative Brad Vocale who cast serious doubts over the legitimacy of a main event broadcast live in Australia, New Zealand and South Africa.

The WBA stipulates its title fights must be contested over 12 three-minute rounds but as far as Vocale was concerned that discrepancy was just the beginning.

"This fight was advertised as a WBA international fight, I have my doubts as to whether it actually was really sanctioned by the WBA," Vocale told Australia's Fox Sports network.

He said a title fight between a novice with just five bouts on his resume (Williams) and an opponent well past his prime (Botha) made a mockery of the WBA belt.

Williams had never fought 10 rounds until Friday night so was not qualified to even challenge for a WBA crown, according to Vocale.

Botha had also lost four of his previous five fights, yet to Vocale's dismay, "All of a sudden they're fighting for a vacant title".

He said the absence of a WBA appointed referee, judge or supervisor at the venue further diminished the legitimacy of the bout. To complicate matters even further, Queensland does not have a legislated body to oversee boxing events - a loophole which can make the state an attractive staging point.

-Sydney Morning Herald, Fairfax NZ