Speaking on ABC News' "Good Morning America Weekend Edition," Dr. Brent Kay said he believes the test was a false positive.
"I've talked to countless doctors in the past couple days (and) everybody has had the same opinion," Kay said. "There's no reason for a professional cyclist to be taking a body-building, mass-building steroid during the Tour de France. Floyd has had some 20 odd tests this year. They've all been normal."
Landis has denied taking illegal drugs, linking his own physiology to the testosterone levels.
"The levels I have had during the Tour and all my career are absolutely natural," he said. He said the night before the test, he had had consumed whiskey and beer.
"I don't know the night before would produce that result," Kay said. "But there's a long list of potential contributors that would cause a false positive test (or) cause the test to look abnormal when, in fact, it's not abnormal." Those would include excessively concentrated urine to a urine sample contaminated by bacteria.
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