Anthony Joshua's United States debut is in serious doubt following reports that his scheduled opponent Jarrell Miller failed a drugs test.
'Big Baby' is set to challenge Joshua for the IBF, WBA and WBO heavyweight titles at Madison Square Garden on June 1 in what would be his first world title bout.
However, Dan Rafael from ESPN broke the news that the undefeated fighter tested positive for the banned substance GW1516, also known as Cardarine and Endurobol, in a Voluntary Anti-Doping Association-conducted urine test.
The results were obtained on March 20 and came to light late in the early hours of Wednesday morning.
Eddie Hearn, Joshua's promoter, took to Twitter to reveal that an "adverse finding" had been discovered in Miller's test, while adding that 'AJ' will continue with his preparations as normal.
Miller's entourage have also confirmed the news, with his co-promoter Dmitry Salita saying the 30-year old will keep training and promised to update us more on the situation.
"We are in the process of obtaining further information about VADA's finding and will have more to say soon on this developing situation," Salita Promotions said on Twitter.
"In the meantime, Jarrell continues to train for his June 1 fight against Anthony Joshua."
GW1516, the substance detected in Miller's sample has been described as "the ultimate endurance enhancing supplement" by bodybuilders in the past and is on the World Anti-Doping Agency's banned list.
If Miller is unable to fight, he will miss out on a fight pursue of at least $4.875 million - comfortably the highest in his career - and that's not even counting broadcasting revenue money from the likes of DAZN and Sky Sports.
Miller failed a drugs test once before during his kickboxing career, being handed a nine-month ban from California State Athletic Commission after methylhexaneamine was found in his system following a urine sample back in 2014.