The people did not want their names used because the doping case against Gay is ongoing and the details have not been made public.
Gay's representatives did not immediately respond to attempts by the AP to reach them.
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, one of the people familiar with the case said.
A first-time offense for doping usually brings with it a two-year ban, though athletes who cooperate with USADA sometimes get reduced penalties.
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.
Gay is cooperating with USADA.
"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. The sample was expected, as he works with us for the fair resolution based on the rules, given the fact of his case."
Gay has been the most-watched U.S. male sprinter for the past several years and has long sold himself as a clean athlete.