Dillian Whyte has been provisionally suspended by the World Boxing Council pending an investigation into an adverse finding in a drugs test prior to his recent bout against Oscar Rivas.
Whyte, who was cleared to fight by UK Anti-Doping and the British Boxing Board of Control, won the WBC's interim title and the right to challenge champion Deontay Wilder after his unanimous decision win.
But the WBC – whose officials say they were not informed of the positive sample before the contest – said in a statement: "A sample UKAD collected from Mr Dillian Whyte in relation with his bout against Oscar Rivas yielded an adverse finding.
"In light of that adverse finding, and pending the outcome of the WBC's own investigation and adjudicatory process, the WBC is provisionally suspending the WBC's recognition of Dillian Whyte as WBC interim world heavyweight champion and mandatory challenger of the division.
"The WBC has notified Mr Whyte and his team of the WBC's suspension and that it will afford Mr Whyte the opportunity to present its position to the WBC at an investigative hearing which will take place at a place and time to be announced in the near future.
"Throughout its investigation and hearing, the WBC will afford Mr Whyte and his team the opportunity to present any available information and materials, and any exculpatory evidence they might deem appropriate."
If any further impropriety is proven, the 31-year-old Londoner, who served a two-year doping ban between 2012 and 2014, could face a lengthy suspension from the sport.
UK Anti-Doping officials have yet to comment on the matter while the British Boxing Board of Control said it deferred its anti-doping programme and sanctions to UKAD.
Last week Whyte wrote on Twitter: "I am so disappointed with the rubbish that has been said about me over the last few days.
"I have lawyers dealing with it and I have been told that I can't talk about it for good legal reasons. I was cleared to fight and I won that fight fair and square. Thanks for the support."
