Whyte landed the WBC interim heavyweight title with a unanimous-decision win over Rivas in London on Saturday.
But Boxing Scene reported on Wednesday that Whyte had "tested positive for one or more banned substances" prior to the fight, which was allowed to proceed by the British Boxing Board of Control (BBBofC).
Whyte's promoter, Matchroom's Eddie Hearn, said in a short Twitter statement that Whyte was cleared to fight following "extensive" testing before the bout by the Voluntary Anti-Doping Association (VADA) and UK Anti-Doping (UKAD).
