Jarrell Miller has reportedly failed a second drugs test which looks set to end his hopes of facing Britain's Anthony Joshua at Madison Square Garden on June 1.
The American was due to fight IBF, WBA, and WBO champion Joshua before an 'adverse finding' from a sample taken on March 20 threw his participation in the bout into doubt.
After being denied a licence to fight by the New York State Athletic Commission, Miller said he had never knowingly taken a banned substance, adding he intended to appeal against the decision to revoke his licence.
Joshua's promoter Eddie Hearn says he has now learned of a second alleged doping violation by Miller, meaning that fight is now all but dead in the water.
"We have now received news from VADA that Jarrell Miller has now failed a second separate test for a further substance. AJ's June 1 opponent will be announced next week - if you don't think you can beat him clean then delete my number!" Hearn wrote on Twitter.
We have now received news from VADA that Jarrell Miller has now failed a second seperate test for a further substance. AJ’s June 1 opponent will be announced next week - if you don’t think you can beat him clean then delete my number!— Eddie Hearn (@EddieHearn) April 19, 2019
A statement released to Sky Sports News later on Friday evening from Jarrell Miller's promoters, Salita Promotions, read: "Salita Promotions and Greg Cohen Promotions are very disappointed in these findings and feel awful that fight fans will be deprived of what would have been a great fight. It's a terrible outcome and unfortunate situation for all parties involved."
The Voluntary Anti-Doping Association (VADA) has been contacted for a response to Hearn's claim.
Joshua, who boasts a perfect record from 22 fights in the paid ranks, will still make his US debut on June 1, with a new opponent expected to be confirmed within the next week.
In his last fight, Joshua earned a seventh-round knockout win against Alexander Povetkin in front of almost 90,000 fans at Wembley Stadium in September 2018.