Conor Benn has failed a drugs test ahead of Saturday's fight against Chris Eubank Jr at the O2 Arena in London, which remains set to go ahead.
Matchroom Boxing and Wasserman Boxing released a joint statement detailing that Benn returned an "adverse analytical finding" for traces of a fertility drug, but has not been charged.
Both boxers also wish to proceed with Saturday's fight.
"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," the statement read. "The B sample has yet to be tested, meaning that no rule violation has been confirmed. Indeed, Mr Benn has not been charged with any rule violation, he is not suspended, and he remains free to fight.
"Mr. Benn has since passed a doping control test conducted by the UK Anti-Doping Agency, the anti-doping authority to which the British Board of Boxing 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."
Sky Sports News has contacted the British Board of Boxing.
Former two-weight world champion Carl Frampton criticised the decision to allow Benn to fight. He wrote on Twitter: "Boxing does itself no favours. There should be no grey areas. If you fail a test you're banned and in my opinion you should be banned for life."
The pair are due to face off almost 30 years since their fathers, Nigel Benn and Chris Eubank Sr, met in the rematch of their iconic rivalry
Eubank Jr has agreed to fight Benn at a catch weight of 157lbs, three pounds lighter than his last fight against Liam Williams in Cardiff earlier this year. The decision recently prompted father Eubank Jr to encourage people to boycott the fight amid concerns over safety.
Fight week media commitments were due to start on Wednesday with the two fighters set to take part in a live workout at a venue in central London.
The media workout was set to begin at 2pm with Benn predicted to enter the ring at 3.25pm and Eubank Jr to follow him 10 minutes later.