US sprinter Tyson Gay failed more than one drug test this year, recording one of his positives at the US championships in June, where he won the 100 and 200 meters.
Earlier this month, Gay revealed he had tested positive in an out-of-competition test he took on May 16.
One person familiar with the case told the AP that multiple positives over a short period of time are a sign of an athlete who wasn't trying to hide anything, but simply didn't know he was taking a banned drug.
The sprinter has already surrendered his spot at next month's world championships. If a positive test from nationals is confirmed by his "B'' sample, those results would be vacated, though it's likely they would be anyway because of his May 16 positive.
The May 16 test has been confirmed by a test of the "B'' sample.
"The additional positive sample is consistent with him taking responsibility," USADA CEO Travis Tygart said. "He should be commended for that and for removing himself from world championships, which we all should appreciate."
Since news of his positive, media reports have linked Gay to Clayton Gibson, an anti-aging doctor based in Atlanta. In an email sent to AP, Gibson would not confirm Gay was among his patients.
The 30-year-old, who won the world championship in the 100, 200 and 4x100 relay in 2007, took part in USADA's "My Victory" program - in which athletes volunteer for enhanced testing to prove they're clean - and his results never raised red flags.
The latest news adds to a slew of negative headlines for athletics. Jamaican Olympic champion, Veronica Campbell-Brown, tested positive for a banned diuretic at a meet on the island in May. A month later, Asafa Powell, former 100m world record holder, tested positive for a stimulant at Jamaica's national championships, as did his teammate, Sherone Simpson, a three-time Olympic medalist.
Gay, finally healthy after years of nagging injuries, was among those expected to push Usain Bolt at worlds next month, but instead of racing in Moscow, he'll be resolving his doping case.