Olympic time trial champion Tyler Hamilton has been suspended by his Phonak team after failing a dope test.
Hamilton may lose the gold medal he won in Athens
The American, who tested positive for blood doping at the Olympics and the Tour of Spain, is waiting for the results of his "B" samples.
"We have to concentrate on the facts. These seem to speak against Tyler," said Phonak boss Andy Rihs.
Rihs added that if Hamilton could not prove his innocence then he would be sacked by Phonak.
Phonak's stance is a complete U-turn from their position on Tuesday, when they gave their full backing to the American.
Hamilton claims he is innocent and says his "B" test results, which are expected on Wednesday, will clear him.
BLOOD DOPING EXPLAINED
What is it?
The administration of red blood cells to increase the blood's oxygen-carrying capacity
Injecting someone else's red blood cells; removing own blood and returning it once body has compensated by making more blood
Why would athletes do it?
The better the oxygen-carrying capacity of the blood, the better an athlete's endurance
Side effects can include:
Blood clots, overload of circulatory system, kidney damage, transmission of infectious diseases
Chances of being caught:
A new test can only detect the practice if the blood comes from a donor
His positive "A" samples suggest that Hamilton had blood from another person put into his body in order to increase his red blood cell count, giving him greater stamina.
If Hamilton's "B" test also shows proof of a blood transfusion, it would mark the first positive blood doping case.
If he is disqualified from the Olympics the gold medal would go to Russia's Viatcheslav Ekimov, with American Bobby Julich moving up to silver and Australia's Michael Rogers taking the bronze.
Hamilton pulled out of midway through the Tour of Spain citing stomach problems.
He acknowledged on Tuesday that that action had been partly because of his positive test.
Hamilton has returned to Switzerland to watch as his "B" sample is tested.