Lawrence Okolie has failed a doping test just a few days before he was due to fight Tony Yoka in Paris.
The 33-year-old had been due to headline on Saturday night against the 2016 Olympic gold medalist in a bout that could have propelled either into world-title contention.
However, Okolie's promoters Queensberry have announced that the former cruiserweight world champion has failed a voluntary test.
"Last night [Monday], 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," a statement read.
"A further update regarding the event will be made in due course."
A decision has not yet been made on the main event, with organisers keen to find a last-minute opponent for Yoka to ensure he still fights on home soil on Saturday.
Okolie took to Instagram to suggest that the adverse finding was due to treatment he has had on an elbow issue in the build-up to the fight.
This was due to be Okolie's fourth fight at heavyweight after stepping up from cruiserweight following his world-title defeat to Chris Billam-Smith in 2023.
Okolie had one fight at bridgerweight, beating Lukasz Rozanski for the WBC title, and then signed a promotional deal with Frank Warren's Queensberry.
He was most recently in action in December when beating Ebenezer Tetteh in Nigeria.
Okolie said in a statement: "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.
"I will of course be fully cooperating with all relevant authorities and I’m confident any investigation will clear my name.
"I won’t be making any further comment at this time. Thank you for all your support and see you soon."
