US sprinter Tyson Gay, the fastest man over 100m this year, has failed a dope test, according to reports in the US media on Sunday, with the 30-year-old immediately withdrawing from the world championships.
Gay, the 2007 world champion, was allegedly informed by the United States Anti-Doping Agency (USADA) on Friday of his failed test. Gay has said he will pull out of August's World Championships in Moscow.
USADA said Sunday that the 30-year-old had removed himself from further competition but that his B sample has yet to be tested so they would not confirm or deny the failed test.
"In response to Mr Gay's statements, USADA appreciates his approach to handling this situation and his choice to voluntarily remove himself from competition while the full facts surrounding his test are evaluated," USADA media relations manager Annie Skinner told AFP.
"The B sample will be processed shortly, and as in all cases all athletes are innocent unless or until proven otherwise through the established legal process, and any attempt to sensationalise or speculate is a disservice to due process, fair play, and to those who love clean sport."
Gay told US media he had made a mistake and been let down by someone else.
News of his failed test quickly spread across social media sites on Sunday with one report claiming he had broken down in tears when speaking of the incident.
Gay had run the fastest time in the world this year at June's US trials in Iowa for the World Championships.
He clocked 9.75sec, the 10th fastest 100m of all time.
With Asafa Powell not having made the Jamaican team for Moscow, the fastest two men over 100m this year will now not be at the worlds.
Gay's personal best of 9.69sec in 2009 makes him the joint-second fastest man ever behind Jamaican legend Usain Bolt and equal with Yohan Blake.
World record holder Bolt's best time over 100m this season is 9.94sec set in Kingston in June.
Gay won the triple of 100m, 200m and 4x100m relay in Osaka in 2007 whilst also claiming a 4x100m silver medal at the London Olympics last year.
Gay, who has also pulled out of next week's Diamond League meeting in Monaco, is not only the American record holder at 100 metres but his time of 19.58 seconds in the 200 metres makes him the fifth fastest athlete in that event.