British sport suffered another body blow last night when it was revealed that Greg Rusedski, the country's second-ranked tennis player, has tested positive for the performance enhancing drug nandrolone.

Rusedski is understood to have been one of a batch of seven players who failed random drug tests last summer, but his identity was protected by the organisers of tennis's professional tour.

The Association of Tour Professionals (ATP) accepted excuses offered by six of the seven players that they had unwittingly taken the drug in supplements given to them by ATP-approved sports medicine staff.

One player, the Czech Bohdan Ulihrach, was named and was banned for two years, fined $43,770 and docked 100 ranking points. The ATP said at that time that the six other players would be dealt with on a case-by-case basis.

Rusedski's positive test has come to light following persistent rumours in the last week that he had failed a drugs test. Last night Rusedski claimed he had never knowingly taken the controversial drug and said that he would prove his innocence at an ATP hearing on February 9th in Montreal.

"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," he said. "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 9th which I shall attend. I fully expect to be found innocent."

Rusedski's claims of innocence will be met with scepticism among a sporting public becoming inured to transgressions of drug regulations by leading athletes.

Last year Dwain Chambers, Britain's leading sprinter, tested positive for the designer steroid THG, and England defender Rio Ferdinand is facing an eight-month ban for failing to take a drugs test.

Rusedski could face a two-year ban if found guilty of knowingly taking the drug, but his eventual fate is far from certain. Tennis's record on drugs is poor compared to many sports, with players receiving shorter bans than they would in athletics.

Following the revelation that seven ATP players had tested positive, it was revealed that approved sports medicine staff had been routinely handing out contaminated supplements.

Mark Miles, chief executive of the ATP, came under threat when it was revealed his organisation had failed to prevent staff from routinely handing out contaminated supplements between August 2002 and May 2003.

At the time David Halman, chief executive of the World Anti-Doping Agency, said he was "disturbed, disappointed and troubled" by the revelations.

Rusedski's fate is clouded by the complex chemistry of nandrolone. It occurs naturally in the body and was found in a large number of sports supplements in the late 1990s and early 2000s, effectively contaminating substances athletes were led to believe were clean.

Olympic 100 metres gold medallist Linford Christie tested positive for the substance and was banned at the end of his career, but maintains his innocence.

For Rusedski the revelation is likely to overshadow a career that has been characterised by underachievement and controversy. Born in Yorkshire but raised as a Canadian citizen, he did not take British citizenship until 1995. His switch energised British tennis and his duels with Tim Henman for the British number one spot gave the sport a profile it had not enjoyed for years.

Rusedski usually came second to Henman, but did reach the final of a grand slam, when he lost the 1997 US Open to Pat Rafter. His greatest contribution to last year's Wimbledon was an expletive-laden outburst in his second-round defeat to Andy Roddick. The controversy that generated will be nothing to this latest storm.

Meanwhile, no traces of THG have been found in any re-tested samples from the 2002 Salt Lake City Winter Olympics, which confirms the belief of experts that use of the new designer steroid has been restricted to a handful of athletes.