Tearful former double sprint world champion Tyson Gay said on Sunday he had tested positive for a substance he could not identify and was pulling out of next month's world championships in Moscow.
Gay, who had the year's fastest 100 meters time of 9.75 seconds, told two reporters in a telephone conference call he was notified by the U.S. Anti-Doping Agency (USADA) on Friday that his A sample from an out-of-competition test on May 16 had returned a positive.
"I don't have a sabotage story. I don't have lies...I basically put my trust in someone and I was let down," said Gay, who added he had never knowingly taken a performance-enhancing drug.
"I made a mistake," added the 30-year-old sprinter from his training base in Amsterdam.
"I am pulling out of Monaco (Diamond League meeting on Friday) and the world championships."
Gay, the world 100 and 200 champion in 2007, said he could not divulge the substance or how the positive occurred.
"I am not allowed to talk about those things right now.
"I know exactly what went on, but I can't discuss it right now," he added.
"I hope I am able to run again," Gay said. "But I will take whatever punishment I get like a man."
USADA said in a statement: "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.
"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 sensationalize or speculate is a disservice to due process, fair play, and to those who love clean sport."
Healthy after years of injury, Gay, the joint second-fastest man in history over 100 meters, had been considered a strong challenger for Jamaican world record holder Usain Bolt at the August 10-18 world championships after winning the American trials in blazing times.
He had put down the year's three fastest 100 times, topped by his 9.75 at last month's U.S. meeting. Only Bolt has run faster than Gay's 19.74 seconds in the 200 this year.
"It has been tough for me," said the soft-spoken Gay. "I have always been a drug-free athlete."
Following his 2007 victories, Gay appeared set to win his first Olympic individual gold medal at the 2008 Beijing Games but the emergence of Bolt and injuries ended that chance.
In 2009, he ran an American record 9.69 seconds, at the time the second fastest ever, but was never fully healthy at ensuing Olympic and world championships.
He finished a heart-breaking fourth at the 2012 London Olympics but won a silver medal in the 4x100 meters relay.
USA Track & Field, the sport's U.S. governing body, said in a statement: "It is not the news anyone wanted to hear, at any time, about any athlete.
"As we approach the world championships, we will remain focused on the competition at hand and winning the right way."
The governing body said it did not know the facts of the case and looked to USADA to adjudicate it and handle it appropriately.