Anthony Joshua's debut fight in the United States could be in doubt after his promoter said the world heavyweight champion's opponent has failed a doping test.

Eddie Hearn says in a Twitter post that Joshua's camp has been informed by the Voluntary Anti-Doping Association that there was an adverse finding in a sample collected from American boxer Jarrell Miller on March 20. Hearn says "we are working with all relevant parties and will update with more details soon." Salita Promotions, which represents Miller, said Wednesday it was obtaining more information about VADA's finding and "will have more to say soon on this developing situation."

Joshua, who holds the WBA, IBF, WBO and IBO belts, is scheduled to fight Miller on June 1 at Madison Square Garden. During the promotional tour for the fight, Miller said both fighters had agreed to between 10 and 12 weeks of drug testing in the buildup to the bout.