Conor Benn FAILS a drugs test
Sportsmail can exclusively reveal the 26-year-old was notified he had returned an adverse finding for the banned substance clomifene.
The substance, which is usually used to treat infertility in women but can increase testosterone in men, is prohibited by the World Anti-Doping Agency. It is understood Benn's test was carried out by the Voluntary Anti-Doping Association.
It is not yet clear whether Benn's situation will trigger a cancellation of this weekend's blockbuster with Eubank Jr, which falls almost 30 years after the second of two iconic fights between their fathers, Nigel Benn and Chris Eubank.
Sources say Eubank Jr still wants the bout to go ahead.
The fight is believed to be worth a six-figure fee to each fighter.
The British Boxing Board of Control, who are overseeing the fight, and Benn's promoter Eddie Hearn have been contacted for comment.
In January, Benn, a welterweight on a rocketing trajectory owing to his perfect 21-0 record, was briefly removed from the WBC world rankings for failing to enrol in their clean-athlete programme.
At the time he said in a statement: 'The World Boxing Council (WBC) have temporarily removed me from their January rankings and have requested in order for me to continue being ranked under the WBC governing body I must officially enrol in the WBC Clean Boxing Program supported by VADA (Voluntary Anti-Doping Association).
'I can confirm I have instructed my team who are now in the process of enrolling me. I wanted to address this personally for the boxing community and my fans.
'It's important to me as a professional athlete to enrol in a clean testing programme and play my part in keeping our sport safe along with having my name stated in top five positions across all governing bodies.'
Benn is currently ranked fifth with the WBC and in the top five with the other three major sanctioning bodies.
Clomifene is listed on both WADA and VADA's prohibited lists under 'hormone and metabolic modulators'.
Benn is moving up almost two weight classes for Saturday's fight against his bigger rival Eubank Jnr.