The 36-year-old failed a drugs test following his draw with Sweden’s Badou Jack, the current World Boxing Council (WBC) champion in the division, in Washington on April 30.

Bute’s positive test was revealed by the WBC after they were notified by the D.C. Boxing and Wrestling Commission.

The 1999 World Championships welterweight bronze medallist now faces a tense wait for the results of his ‘B’ sample as, if that comes back positive, his career in the sport could be over.

Ostarine, which has been on the World Anti-Doping Agency banned list since 2008, is used as a muscle waster, helping to increase the muscle mass, improve stamina and boost recovery ability, though it is not an anabolic steroid.

Bute, who was the International Boxing Federation champion for five years from 2007 to 2012, has always been a staunch advocate of anti-doping and his protested his innocence despite his doping failure.

His trainer, Howard Grant, has even suggested he "honestly believes" it could be the result of sabotage.

“I am surprised and distressed by this news,” Bute said.

“I do not understand what may have led to this positive result.

“I always passed all the required exams since I was world champion.

“More recently, in preparation for my clash against [Britain’s James] DeGale in Quebec City last November, I was tested eight times at the start of my camp until my fight.

“I did not take anything and I never used banned substances and I have full confidence in my team.

“There will be an analysis of the B sample and I am confident it will be negative.”

His promoter, Yvon Michel, said he was “surprised by the preliminary results” and maintained he would be “fully behind” his athlete as he bids to clear his name.

The news follows that Russian boxing star Alexander Povetkin had shown traces of meldonium in a doping sample, which effectively forced the cancellation of his WBC heavyweight title fight with United States rival Deontay Wilder.