Anthony Joshua's bout against Jarell Miller might be called off after the American was denied a license to fight by the New York State Athletic Commission, following an adverse finding from a drug test in March.
Miller is said to have tested positive for the banned muscle growth substance GW1516, a metabolic modulator also known as cardarine and endurobol, from a test sample that was taken on 20 March.
"The New York State Athletic Commission has denied Jarrell Miller's professional boxing license application for a violation relating to the use of a prohibited substance. We have no further comment at this time," the commission said in a statement.
While the decision to deny Miller a license to fight is fatal, it does does not guarantee that the fight against AJ is off.
The fight could still be on if Miller's B sample does not show an adverse finding, as he would be able to reapply.
Joshua's promoter Eddie Hearn is, however, making moves already, in case it becomes official that the fight cannot go on.
The Matchroom boss revealed he was already "on the search for a new opponent".
"Literally anyone can get it. There are some names that would appeal to our partners -- DAZN, Sky Sports and Madison Square Garden -- more than others and it's our job to get the ones that appeal most. I've spoken to 16 heavyweights in the last 24 hours, 10 of which are not suitable," he said.
Miller has previously served a nine-month ban from the California State Athletic Commission while he was kickboxing in 2014 after testing positive for methylhexaneamine.
The undefeated American is set to lose millions of dollars if he is eventually ruled out of the fight.