The British Boxing Board of Control says Saturday’s fight between Conor Benn and Chris Eubank Jr is “prohibited and not in the interests of boxing”.
Benn, 26, has returned an “adverse analytical finding for trace amounts of a fertility drug”, promoters have said.
They say he has not been suspended and is free to fight Eubank, 33, in London as his B sample has yet to be tested.
But British boxing’s governing body has issued a statement that places the all-British fight in doubt.
The board said its decision not to sanction the fight was communicated to the boxers and promoters on Wednesday morning.
Benn said he had spoken to Eubank, they had both taken medical and legal advice and “want the fight to happen for the fans”.
“He believes in me. It’s not who I am, it’s not what I’m about. He was understanding,” Benn added.
“Throughout my whole career I’ve never had any issues before. I’m a clean athlete and we’ll get to the bottom of this.”
Eubank said he was ready to fight, although added: “There was no phone call. We haven’t spoken since this has been announced.”
Benn’s promoter Eddie Hearn, of Matchroom Boxing, told BBC Sport: “As we stand right now, the British Boxing Board of Control is not sanctioning the fight.
“That does not mean the fight is off, but there is a process we have to go through.
“Conor Benn is not suspended, he is free and clear to fight. There’s lots going on with the lawyers.”
A statement earlier on Wednesday from promoters Matchroom and Wasserman Boxing said Benn had not been charged or suspended and that he and Eubank are still keen to fight.
The pair are scheduled to meet in a catchweight bout at the O2 Arena, 30 years after their fathers, Nigel Benn and Chris Eubank Sr, faced each other in the ring.
The promoters’ statement said: “We have been made aware that a random anti-doping test for Conor Benn conducted by the Voluntary Anti-Doping Association returned an adverse analytical finding for trace amounts of a fertility drug.
“Mr Benn has since passed a doping control test conducted by the UK Anti-Doping Agency, the anti-doping authority to which the British Boxing Board of Control has delegated its doping control testing for the bout. Mr Benn has passed all doping control tests conducted by Ukad.
“Both fighters have taken medical and legal advice, are aware of all relevant information and wish to proceed with the bout this Saturday.”
It is conceivable the promoters could find another body to sanction the bout.
A fight between David Haye and Derek Chisora was sanctioned by the Luxembourg Boxing Federation 10 years ago despite neither boxer having a licence at the time.
“It’s been done before and it’s not something I’ve looked at before or something I necessarily agree with,” said Hearn.
“But at the end of the day there has to be some harsh conversations with the board to understand what the process is moving forward.
“This is not a situation where we want to run rogue and come up with an alternative plan. We want our governing body to be comfortable.”
Benn tested positive for the female fertility drug clomifene at the end of August or beginning of September, said Kalle Sauerland of Wasserman Boxing, the promoters who represent Eubank.
The drug, also known as clomiphene, is on the World Anti-Doping Agency’s list of banned substances.
Sauerland told Talksport he did not regard it as a performance-enhancing drug but said “it can raise testosterone”.
“We discussed it straight away with the most important person from our side, the athlete,” he said.
“He was happy to continue and spoke to Benn directly.”
A 157lbs limit has been put in place for the catchweight bout.
Eubank Jr faces the task of dropping down from 160lbs, where he has spent most of his career, while Benn was 146.5lbs when he beat Chris van Heerden in April.
Failure to make the contracted weight by either fighter on Friday would result in a £100,000 fine for each pound recorded over the limit.
“All I can do is be a professional and make sure I’m ready to fight. I’ve done my job. It’s now in the hands of the promoters, governing bodies,” Eubank told Matchroom’s YouTube channel.
“Of course there’s concerns. I’m a clean fighter, I’m prepared, I’ve cut the weight and I’m ready to go.”
Eubank and Benn’s fathers famously met twice in the 1990s, with the former winning the first fight and the rematch ending in a draw.
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