American Tom Danielson has revealed he failed a doping test for synthetic testosterone but the Cannondale-Garmin rider denies taking a banned substance.

"While I was eating dinner with my team the night before Tour of Utah I received a call from USADA notifying me that a out of competition test I gave July 9th has tested positive for, from what I understand, synthetic testosteron," Danielson said on Twitter.

"I have not taken this or any other banned substance."

Danielson was handed a six-month ban in 2012-13 after admitting to blood doping while riding with The Discovery Channel team. The 37-year-old said he would skip the Tour of Utah, which starts on Monday. He won the race the last two years.

"I feel incredibly hurt, frustrated, and angry by this. I don't understand how or why this happened and still can't even accept this is true," added Danielson, who placed eighth in the 2011 Tour de France.

“I would never ever take anything like this especially after everything I have gone through the last years. This makes absolutely no sense. I will now, as I wait for the B test, have the supplements I take, tested to see if this is what caused it,” he further wrote on the micro-blogging site.

Image: Tom Danielson of the United States riding for Garmin Sharp

Photograph: Doug Pensinger/Getty Images