German cyclist Patrik Sinkewitz says he thought his positive test for human growth hormone was "a joke."

In an interview with German newspaper Sueddeutsche Zeitung published Monday, Sinkewitz denied he took banned substances despite becoming the first cyclist to test positive for HGH.

The International Cycling Union announced Friday that Sinkewitz tested positive for HGH at the Grand Prix di Lugano on Feb. 27. He could face a lifetime ban because he already has served a one-year doping suspension.

"I thought at first that it was a joke," Sinkewitz told the Sueddeutsche newspaper. "But then I got it in writing."

"I can only say that I did not take any banned substances," Sinkewitz told the paper.

Sinkewitz said he had requested a test of his "B" sample.

"The fact is that they found a substance in me. Now I have to find out how that could be," Sinkewitz said.

Sinkewitz tested positive for testosterone in an out-of-competition test before the 2007 Tour de France and was fired by his T-Mobile Team. He was banned for one year, half the usual suspension because he cooperated with German investigators and shared details about doping in cycling.

The rider's Italian team, Farnese Vini, said it was "not responsible" for the positive test and was prepared to fire Sinkewitz if he is found guilty of doping.

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