U.S. sprinter Mickey Grimes has failed a doping test for a banned substance, a source told Reuters on Friday.

The source, who has knowledge of the case, refused to name the substance.

The Chicago Tribune reported on its website that Grimes had failed a test for norandrosterone in out-of-competition testing by the International Association of Athletics Federations (IAAF) on May 25 in Los Angeles. IAAF officials did not return telephone calls on Friday.

Grimes faces a lifetime ban if found guilty of a doping violation since it would be his second positive. He was stripped of his 2003 Pan American Games 100 metres gold medal after testing positive for the stimulant ephedrine.

His agent Emanuel Hudson would not confirm the positive test. "I can not confirm or deny that," Hudson told Reuters.

Grimes is the third member of HSInternational reportedly to have failed a doping test.

Published reports on Friday said hurdler Larry Wade had also tested positive for norandrosterone. Sprinter Torri Edwards confirmed on Thursday she had tested positive in April for a stimulant that could keep her out of next month's Olympic Games in Athens.

Edwards was runner-up in the women's 100 metres at the U.S. Olympic trials last week. She is considered one of the favourites in the 200 metres this weekend.

Wade withdrew from the trials on Friday with an injured arm.

Grimes was eliminated in the semi-finals of the 100 metres on Sunday.