Amir Khan's rematch against Lamont Peterson has been thrown into doubt after the American failed a drug test for a banned substance.
Khan had been set to meet Peterson on May 19 in Las Vegas, five months after losing his WBA and IBF light-welterweight world titles in a controversial points decision in the pair's original bout in Washington DC.
Peterson's lawyer confirmed that the fighter had registered a preliminary positive test as part of the Voluntary Anti-Doping Association procedures that Peterson himself had suggested the fighters undergo.
"We have tremendous respect for VADA and its mission. Lamont, Barry (Hunter, his trainer) and the entire team emphatically support random drug-testing in the most comprehensive manner possible.
"We are working expeditiously with a team of pathologists and other medical specialists. Lamont has never had a positive test either before or after this isolated occurrence and we plan to submit medical findings by close of Tuesday reflecting the actual facts in support of Lamont's good faith intentions and the requirements of the commission."
Early reports suggest that Lamont had tested positive for synthetic testosterone, which can be used to boost muscle strength and reduce recovery time.
There is no evidence of wrongdoing at this stage and Khan's manager Asif Vali said that Peterson's camp are confident that the American will be exonerated and that the fight will go ahead as planned.
"The Peterson team seem to think that something's gone wrong during the very first VADA drug test which Lamont took in March. Their explanation is that it's something he took earlier on in the year - before the last fight," he said, adding that Khan was "very disappointed" about the news.
"(As things stand) the fight's on. Obviously the Nevada commission will come back to us with their findings. They'll look at things quite in depth before they make a final decision...
"We've had no concrete clarity as yet... we'll find out more in the next 24 hours (as of 10am UK time)."
