Adidas on Monday suspended its sponsorship of Tyson Gay after the American sprinter returned a positive doping test.
The sportswear giant acted a day after Gay disclosed that a banned substance was detected in an out-of-competition test in May and he had pulled out of next month's world championships in Moscow.
"We are shocked by these recent allegations, and even if we presume his innocence until proven otherwise, our contract with Tyson is currently suspended," Adidas said in a statement.
The 30-year-old Gay, the American record-holder in the 100 meters, has been backed by Adidas since 2005.
"During this time he has been a great ambassador for the sport of track and field and our brand," Adidas, which is based in Herzogenaurach, Germany, said.
The shoe and sports clothing maker is invoking the clause in Gay's contract relating to doping.
"Adidas has a clear policy on doping and drug use," the company said. "Each of the agreements with our athletes include a clear clause which states that the agreement shall be terminated by Adidas if the athlete is found guilty of the possession or use of drugs or any other prohibited substance by the relevant governing sports body having jurisdiction over the athlete."
Gay, who won the 100- and 200-meters at U.S. national championships last month, has said he will have his "B'' sample tested soon, possibly as early as this week.
He has not disclosed the banned substance that led to the positive test, but said he put his "trust in someone and I was let down."
"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 Sunday, referring to the U.S. Anti-Doping Agency.
Results for Gay, who won the 100, 200 and 4x100 relay at the world championships in 2007, never raised red flags until an out-of-competition test on May 16.