American sprinter Tyson Gay has tested positive for a banned substance and has pulled out of next month's World Championships.
Gay, the world's second fastest man over 100m, said he was notified by the US Anti-Doping Agency on Friday that his A sample from an out-of-competition test in May had returned a positive.
His B sample is yet to be tested.
"I don't have a sabotage story... I basically put my trust in someone and was let down," said Gay, 30.
"I made a mistake. I am pulling out of Monaco (this week's Diamond League meeting) and the World Championships."
The 2007 world champion has clocked the three fastest times of this year. Usain Bolt is the only athlete to ever run faster than Gay's 9.69 personal best.
Gay won the 100m at the Jamaica Invitational athletics meeting in May with a time of 9.86 seconds, before clocking 9.75 seconds - the fastest time of 2013 - to win the US World Championships trials the following month.
Gay's preparations for August's World Championships in Moscow continued with victory in the men's 100m at the Diamond League meeting in Lausanne, running 9.79 seconds.
He has suffered with injuries in recent years. A hip injury forced him to withdraw from the 2011 US world trials 100m semi-finals, before the subsequent surgery ruled him out of running for the rest of the year.
He returned to the track in 2012 and qualified for the 100m at the London Olympics by finishing second in the US Olympic trials to Justin Gatlin.
Gay, who also runs at 200m, then won the 100m at both the Paris and London legs of the 2012 Diamond League before coming fourth at the Games in London.