The fight is due to take place on 1 June at New York’s Madison Square Garden and act as Joshua’s debut in the United States. Both camps have been informed of the adverse finding, which was discovered from a random Voluntary Anti-Doping Association-conducted (Vada) urine test Miller gave on 20 March.
Miller has accused British heavyweight Joshua of using performance-enhancing drugs during their build-up towards the fight.
Miller’s co-promoter, Dmitriy Salita, said that the American’s camp have been informed about the adverse test result and are in the process of trying to obtain more information.
“We are in the process of obtaining further information about Vada’s finding and will have more to say soon on this developing situation. In the meantime, Jarrell continues to train."
Joshua’s promoter, Eddie Hearn, added: "We have been informed by Vada that there has been an adverse finding in Jarrell Miller's sample collected on March 20th, 2019.
"We are working with all relevant parties and will update with more details soon. AJ's preparation continues for June 1st at MSG (Madison Square Garden)."
Miller was kickboxing in 2014 when he tested positive for methylhexaneamine in a urine sample and was suspended for nine months by the California State Athletic Commission.
Both boxers confirmed during their promotional tour for their scheduled fight that they had committed to between 10 and 12 weeks of drugs testing in the lead-up to the bout in an effort to kerb the talk of performance-enhancing drugs, which was threatening to overshadow the heavyweight title contest.
"I am on (drug testing scheme) ADAMS whereabouts, they have to know where I am for an hour every day and could walk in anytime,” Joshua said previously.
"They can turn up any time during the day and that is a lifetime commitment. I have been on that since 2012 and I pay £40,000-a-fight to be tested by Vada two times a week."
Joshua and Miller were due to fight for the WBA, IBF, WBO heavyweight titles in New York, but that bout is now in serious jeopardy.
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