Boxer Tyson Fury is at the centre of a drugs investigation after traces of a banned steroid were reportedly found in a sample.
The world heavyweight champion could lose his three title belts and be suspended from the sport if he is found guilty of doping.
Levels of nandrolone, which helps muscle growth, were said to have been found in a sample, which was taken between February and March last year - months before he beat Wladimir Klitschko for the world title.
Nandrolone is also produced in the body, but the volume found in Fury's sample was deemed unacceptable, according to the Daily Mirror.
Fury's cousin Hughie is also a boxer and tested positive for the substance as well.
The pair were reportedly told about the findings in September last year, but both deny doing anything wrong.
They are due to appear at a panel hearing to explain why the traces of the substance were allegedly discovered.
A spokesman for Team Fury said: "We are baffled by today's story in the Sunday Mirror. Tyson Fury absolutely denies any allegation of doping."
In November, Fury admitted the sport needed to tackle the problem of drugs.
He said: "Boxing has a big problem with drugs. But it doesn't bother me because at the end of the day it's about determination."
Eyebrows were raised on Friday when Fury pulled out of his world heavyweight title rematch with Wladimir Klitschko citing an ankle injury.
But his TV paymaster Frank Warren has confirmed the ankle injury is genuine and the fight will be rescheduled.
Suspicions initially ran deepest in the Austrian Tyrol where Klitschko has been training intensively for his bid to regain the championship belts which Manchester's Gipsy King prised from him in a huge upset in Germany.
However, the man who dominated the heavyweight division for a decade has accepted the delay, saying: "Of course I am currently totally disappointed. I also feel sorry for my fans who were very excited. But this just means I'll get my belts back a few weeks later."
The new working date is October 29, again at the Manchester Arena.
Warren, despite his own disappointment at a cancellation so close to the fight date of July 9, reports that Fury has no option but to withdraw.
As Fury posted pictures of his bruised and swollen ankle on his Instagram site, Warren, head of the BoxNation subscription channel, said: "There is no way Tyson could have boxed in the next couple of weeks. He went over on the ankle while running. We're all gutted this has happened. It has cost us a fortune but we will get it back on."