The world heavyweight champion Tyson Fury, who last week pulled out of his proposed rematch with Wladimir Klitschko citing mental health issues, has reportedly tested positive for cocaine.

Fury, who holds the WBA and WBO world titles, was said to have been informed on Thursday night that his A sample from a random urine test on 22 September had tested positive for the substance benzoylecgonine, the central compound found in cocaine. Fury pulled out of the rematch a day after the test.

The news was broken by ESPN, which quoted a letter from the Voluntary Anti-Doping Agency (Vada) president, Dr Margaret Goodman, to representatives for Fury, Klitschko, the British Boxing Board of Control and the United States’ Association of Boxing Commissions. In it Goodman wrote: “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 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.”

However in an email to the Guardian, Goodman said that Vada would not be commenting on story and that they “do not release results publicly unless requested by the athlete”. Even if the positive test is confirmed Fury is unlikely to face a ban from competing as cocaine is not prohibited when it is taken out of competition under World Anti-Doping Agency rules. However with the WBO having requested he provide evidence that he was “mentally unfit” to fight against Klitschko by Wednesday, and the IBO having also asked him for a medical report, the 28-year-old from Morecambe still faces the prospect of losing one or more of his world title belts before he next steps in the ring. Separately Fury also has a UK Anti-Doping investigation hanging over him after a sample tested positive for the anabolic steroid nandrolone last year. However he denies any wrongdoing and is contesting those charges.

Fury won the world title with a convincing points victory over Klitschko last November but since then he has made headlines for what he has done outside the ring. His rematch against Klitschko was originally due to take place in Manchester during the summer but Fury pulled out citing an ankle injury. Earlier he had admitted he was five stone over his fighting weight having eaten and drunk to excess.

The fight was then rescheduled for 29 October but doubts were raised about it going ahead when Fury didn’t show up for the press conference in London on 10 September, claiming that his car had broken down on the motorway and his phone battery had also died. Those fears were realised less than a fortnight later when Fury was declared medically unfit to fight.

Bernd Bönte, Klitschko’s manager, responded to the cocaine claim by telling ESPN: “I think Fury is probably the most unworthy heavyweight champion in history, not only because of this situation but because of the whole package of his sexist comments, his antisemitic comments and his homophobic comments that have been [well documented].”

It was widely reported that Fury had severe depression, with a statement from Hennessy Sports saying he was “devastated” when the rematch was called off. A statement released last week added: “Medical specialists have advised that the condition is too severe to allow him to participate in the rematch and that he will require treatment before going back into the ring. Tyson will now immediately undergo the treatment he needs to make a full recovery.”

Neither Fury’s representatives nor the BBBC were available for comment when contacted by the Guardian. A Ukad spokesperson said: “UK Anti-Doping will not discuss or disclose information relating to cases, until due legal process has been completed.”