The reigning World Heavyweight champion previously withdrew from his rematch against Wladimir Klitschko
Tyson Fury is facing fresh questions about his boxing future after it emerged he failed a drugs test.
The Fury camp has refused to comment on the reports, however the World Boxing Organisation (WBO) is taking an interest in the allegations involving its world heavyweight champion.
It has been widely reported Fury tested positive for cocaine, with ESPN saying the positive test came after he gave a urine sample on 22 September.
The US-based sports broadcaster said Fury was tested in Lancaster by the Las Vegas-based Voluntary Anti-Doping Association (VADA), as part of the routine agreed by both him and Wladimir Klitschko before their fight.
The pair had been due to square off in Manchester on 29 October, with Fury defending the WBA and WBO heavyweight belts he won against the Ukrainian last November, but that clash was postponed on 23 September.
Cocaine, while being an illegal Class A drug, is not banned out of competition.
Sources have told Press Association Sport the VADA test was taken on an in-competition basis.
A spokesman for Hennessy Sports, Fury's promoter, declined to discuss the ESPN report.
A source close to the postponed fight told PA he had been told "traces" of cocaine were found in Fury's system, something the 28-year-old fighter's camp would not confirm.
When contacted regarding Fury, VADA said it does not release the results of samples unless at an athlete's request.
WBO president Paco Valcarcel told PA his organisation was waiting to see the paperwork involved in the tests before making any decisions.
He said: "We have to wait for the British board to notify us of the information they have got regarding the doping tests."
Asked whether Fury risked losing his WBO belt, Valcarcel added: "We don't want to go any further until we receive the medical certification and the results."
ESPN said it had obtained a letter from VADA president Dr Margaret Goodman that it said was sent to both fighters, plus the British Boxing Board of Control and the United States' Association of Boxing Commissions on Thursday.
It said the letter read: "This letter is to advise you that the 'A' sample urine specimen number 4006253 collected from Tyson Fury on September 22, 2016 in Lancaster, England through his participation in the Voluntary Anti-Doping Association (VADA) program has been analysed for anabolic agents, diuretics, beta-2 agonists, stimulants and drugs of abuse.
"The results of the analysis are as follows: Adverse. Urine specimen contains benzoylecgonine.
"Mr Fury has the right to promptly request analysis of the 'B' sample at his expense."
Benzoylecgonine is a metabolite of cocaine.
It is unclear whether Fury will lose his belts, having failed to make a title defence this year.
After the cancellation of a previous fight with Klitschko scheduled for 9 July, it emerged the UK Ant-Doping Agency (UKAD) had charged Fury over a urine sample taken in February 2015, and his cousin Hughie with a doping offence.
They deny wrongdoing.
It was alleged the sample - taken nine months before Fury beat Klitschko - contained traces of the banned substance nandrolone.
Fury was provisionally suspended, but the ban has since been lifted, and his legal team said they would be suing UKAD over the allegations.
A hearing will be held in November.