Lawrence Okolie has failed an anti-doping test ahead of his scheduled fight against Tony Yoka this weekend.
Okolie had been due to fight Olympic gold medallist Yoka in Paris on Saturday.
Queensberry promotions said on X on Tuesday morning: "Last night, the Voluntary Anti-Doping Association [VADA] informed Queensberry that Lawrence Okolie returned an adverse finding following an anti-doping test conducted ahead of the show in Paris this Saturday."
The promoter has cancelled the event that was due to take place at the Adidas Arena in the French capital.
It was a pivotal contest for the Londoner's career. No 1 ranked with the WBC, Okolie was hoping to position himself for a shot at that heavyweight world championship.
Now that fight has been called off and Okolie will try to exonerate himself.
Okolie was a world champion at cruiserweight. He picked up a WBC belt in the new bridgerweight division before moving up again and was on a run of three victories at heavyweight.
On social media Okolie said: "Before anyone starts imagining the worst, following my bicep injury last year, I sustained an elbow injury on the same arm during this camp. I had a treatment on it and now we are here.
"I truly hope sense prevails."
He added: "I will of course be fully co-operating with all relevant authorities and I'm confident any investigation will clear name.
"I won't be making any further comment at this time. Thank you for all your support and see you soon."
Your Site News has contacted VADA for comment.
