Adidas has suspended its contract with Tyson Gay after the former double world sprint champion failed an out-of-competition dope test.
"We are shocked by these recent allegations and, even if we presume his innocence until proven otherwise, our contract with Tyson is currently suspended," a spokesman for the German sportswear company said on Monday.
Adidas' agreements with athletes give it the right to terminate the contract "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", Reuters reports.
Gay, who has been on Adidas' books since 2005, said on Sunday he had tested positive for a substance he could not identify and that he was pulling out of next month's world championships in Moscow.
"I don't have a sabotage story. I don't have lies ... I basically put my trust in someone and I was let down," the American said, adding that he had never knowingly taken a performance-enhancing drug.
Also on Sunday, former world 100m record holder Asafa Powell and Olympic 4x100m relay silver medallist Sherone Simpson both said they had tested positive for the stimulant oxilophrine at last month's Jamaican championships.
Powell and Simpson, both from Jamaica, have denied knowingly taking a banned substance.
The doping cases are a blow to the image of athletics a month ahead of the world championships in Moscow, with the sport struggling to maintain a high profile outside Olympic years.