Greg Rusedski, Britain's number two tennis player, has tested positive for the banned drug nandrolone.
He says he is convinced that he will be cleared when it comes to a tribunal in Montreal next month.
In a statement Rusedski's said: "In response to media inquiries I confirm that I have been advised by the ATP anti-doping administrator that a sample I provided tested positive for a low concentration of nandrolone metabolites.
"I wish to make it clear that I do not and never have taken performance enhancing drugs.
"This is a very complex situation which once understood will clearly demonstrate my total innocence.
"There is a hearing to be held in Montreal on February 9 which I shall attend. I fully expect to be found innocent."
It is believed the test dates from a tournament he played in July in Indianapolis, a month before he made a disappointing first round exit from the US Open at the hands of France's Gregory Carraz.
On the court, he crashed out of his first tournament since returning from injury.
Rusedski lost his second round match in straight sets 6-2 6-2 to unseeded Cyril Saulnier of France at the AAPT Championship in Adelaide.
He made a winning return to action in the first round, beating Stanislas Wawrinka of Switzerland 6-4 6-2 in a rain-interrupted match spanning two days.
Rusedski had been on the sidelines since losing both his singles matches in last September's Davis Cup defeat in Morocco.
The 30-year-old injured his back in that tie to cap a disastrous 2003 which also saw him suffer foot and knee problems.
He says he is convinced that he will be cleared when it comes to a tribunal in Montreal next month.
In a statement Rusedski's said: "In response to media inquiries I confirm that I have been advised by the ATP anti-doping administrator that a sample I provided tested positive for a low concentration of nandrolone metabolites.
"I wish to make it clear that I do not and never have taken performance enhancing drugs.
"This is a very complex situation which once understood will clearly demonstrate my total innocence.
"There is a hearing to be held in Montreal on February 9 which I shall attend. I fully expect to be found innocent."
It is believed the test dates from a tournament he played in July in Indianapolis, a month before he made a disappointing first round exit from the US Open at the hands of France's Gregory Carraz.
On the court, he crashed out of his first tournament since returning from injury.
Rusedski lost his second round match in straight sets 6-2 6-2 to unseeded Cyril Saulnier of France at the AAPT Championship in Adelaide.
He made a winning return to action in the first round, beating Stanislas Wawrinka of Switzerland 6-4 6-2 in a rain-interrupted match spanning two days.
Rusedski had been on the sidelines since losing both his singles matches in last September's Davis Cup defeat in Morocco.
The 30-year-old injured his back in that tie to cap a disastrous 2003 which also saw him suffer foot and knee problems.
