A member of the Alinghi sailing team has been banned from the sport for two years after testing positive for cocaine.
The Court of Arbitration for Sport in Lausanne upheld an appeal by the World Anti-Doping Agency, which asked for 49-year-old Simon Daubney to be suspended.
"The objective presence of cocaine metabolites in Mr Daubney's urine samples is undisputed," the panel said. "Daubney has not established that he bears no significant fault or negligence."
It added that America's Cup officials had wrongly cleared the New Zealand sailor, who tested positive before last year's Cup, which Geneva-based Alinghi went on to win 5-2 over New Zealand.
It was the first failed doping test in the competition's 157-year history.
Daubney has denied knowingly taking the drug and says he has passed polygraph tests conducted by European authorities. The Swiss Olympic Association and International Sailing Federation backed him.
The decision was backdated to July 14, 2007. Alinghi's victory is not affected.
The team of billionaire Ernesto Bertarelli has been locked in a legal battle with the United States-based team, Oracle, over the particulars of the next race.