British world heavyweight champion Tyson Fury has denied doping, after the Sunday Mirror said he was being investigated by UK Anti-Doping.
The newspaper says traces of a banned anabolic steroid were allegedly found in a sample given by Fury last year.
The boxer's promoter, Hennessy Sports, says it is "baffled" by the story.
Undefeated Fury, 27, this week postponed his rematch with Wladimir Klitschko after injuring an ankle during training.
Hennessy's statement said that fight, originally scheduled for 9 July, will now take place in October.
Fury beat Ukrainian Klitschko, 40, in November to win the WBA and WBO heavyweight titles.
The Sunday Mirror reports "unacceptable levels of nandrolone" were found in a sample taken from Fury in the lead-up to that fight.
Nandrolone, which is produced naturally in the body in small amounts, can increase muscle growth and reduce tiredness.
Ukad says it refuses to discuss cases "until due legal process has been completed".
The British Boxing Board of Control is aware of the investigation, according to the Sun.