US sprinter Gay, who is the joint second-fastest 100m runner of all time behind Usain Bolt, withdrew from the World Championships in Moscow after being notified of a positive doping control at the national trials, before failing a second out-of-competition test in May.
The substance involved was not disclosed, although Gay accepted responsibility for the test, saying a member of his backroom staff had let him down and that he would fully co-operate with authorities.
The BBC claims to have seen a letter from the US anti-doping authority (USADA), which said: "Using the Carbon Isotope Ratio Analysis it reported that the sample had an adverse analytical finding reflecting values that are consistent with the administration of a steroid of exogenous nature."
Carbon isotope radio analysis can be used to test for a wide range of substances, although in sports anti-doping it is particularly useful to detect testosterone and its precursors.
"I don't have a sabotage story," Gay said after pulling out of the Worlds.
"I basically put my trust in someone and was let down. I know exactly what went on, but I can't discuss it right now."
Gay has worked with Atlanta chiropractor and anti-ageing doctor Clayton Gibson, who insists his clinic only uses “food-based” products with its athletes, although it is unclear whether he is the backroom staff member referred to by the 30-year-old former world champion and 2012 Olympic silver medallist.