British heavyweight and WBC mandatory challenger Dillian Whyte has reportedly tested positive for a banned substance, with the news coming just days after he became the mandatory challenger.
Whyte had long held the number one ranking for the WBC title but finally became mandatory last Saturday by beating Oscar Rivas, in a hard fought fight.
However Boxing Scene report that the A sample of a test taken out by UK Anti Doping, UKAD, found traces of one or more banned substances, with the test taken prior to last weekend's fight.
The report claims that the Whyte camp, including representatives Matchroom Boxing, were aware of the positive test, with the results being returned on July 17th.
The British Boxing Board of Control allowed the fight to go ahead with UKAD rules saying that until the whole process in complete, including any appeal, there can be no sanctions.
Whyte will have to wait for the results from his 'B' sample, although it's rare that the results change between the two samples.
It is not the first time that the British fighter has failed a drugs test with the 31-year-old being banned for two years in 2012 after testing positive for Methylhexaneamine.
The fight with Rivas last weekend was for the WBC heavyweight interim title after Whyte had been the organisation's number one contender for over 600 days.
Whyte, whose only professional loss came at the hands of Anthony Joshua in December 2015, weighed in ahead of the fight at 18st 2lbs, over a stone heavier than his opponent and heavier than he usually goes into a fight.
His height and weight advantage allowed him to dominate the impressive Rivas for most of the rounds, but he was knocked down in the ninth.
Despite the 10-8 round Whyte, who had most recently beaten Dereck Chisora for a second time before the Rivas fight, won on a unanimous decision, with the cards reading 15-112, 115-112, 116-111.
With the interim title in hand and the mandatory position secured it was expected that the Jamaican born Brit would face the winner of Deontay Wilder and Tyson Fury around May next year.
Wednesday's news throws that into serious doubt.