The American 100-meter record holder is the second-fastest man in the world and promoted anti-drug athlete.
Adidas ended their sponsorship contract with Gay shortly after the news broke.
"We are shocked by these recent allegations," a spokesman for Adidas said Monday. "Even if we presume his innocence until proven otherwise, our contract with Tyson is currently suspended."
Gay said he will pull out of the world championships next month in Moscow.
Two other runners, Jamaicans Sherone Simpson -- an Olympic gold medalist and two-time silver medalist -- and Asafa Powell, the record-holder before Gay and fourth-fastest man in history, tested positive for banned stimulants.
Gay was notified last week that he had failed the test with the U.S. Anti-Doping Agency, and he will have a second test as early as this week. Gay did not reveal which banned substance he had used, nor who provided it to him.
He admitted it shortly after rumors arose on LetsRun.com, a site known for posting accurate rumors, posted about the test.
"I don't have a sabotage story. I don't have any lies. I don't have anything to say to make this seem like it was a mistake or it was on USADA's hands, someone playing games," Gay said. "I don't have any of those stories. I basically put my trust in someone and I was let down."