The sport is facing the threat of a High Court action against its governing body following a newspaper allegation that Mats Wilander and Karel Novacek tested positive for cocaine at the French Open last June.
The International Federation would neither confirm nor deny a News of the World story yesterday stating that Wilander, a former world No 1, and Novacek had denied using drugs, had consulted lawyers, and would challenge the validity of the tests.
The News of the World carried the following statement from American lawyers acting for the players: "On behalf of our clients, we categorically deny the allegation. We have lie detector evidence proving our clients are telling the truth in denying the allegation.
"We came to London with our clients and our expert witnesses to prove our clients' innocence, as the ITF rules require. The ITF then cancelled a hearing at 11.55pm the night before the hearing was to begin.
"As a result, we are issuing proceedings against the ITF in the High Court in London next week. A more complete statement will be issued by our clients in due course."
Wilander and Novacek, who withdrew from the Australian Open saying they were injured, were in London last week, reportedly for meetings with Dr David Martin, the head of the sport's co-ordinated anti-doping programme, Gavin Applebee, of the ATP Tour, and Debbie Jevons, of the ITF.
Cocaine is a class 2 prohibited substance on the tour. Positive test results subject a player to a three-month suspension for a first offence, a one-year ban for a second offence, and permanent suspension for a third.
"My first reaction is that someone wants to spread a nasty rumour about [Wilander]," the Swedish Federation president Jan Francke said. "It seems incredibly strange considering what kind of person Mats is. I'm a member of the ITF board and I would have known if this had happened. Since the French Open took place six months ago I would have heard something about this."
Wilander, 32, followed Bjorn Borg in the dynasty of Swedish champions and is one of the sport's most respected players. Having gradually drifted out of the game after winning three of the four Grand Slam titles in 1988, he revived his interest and in the past two years has elevated his ranking from No 326 to No 45.
The Czech Novacek, 30, now resident in Monte Carlo was ranked as high as No 8 in the world in 1991, but slumped to No 122 last year.
"I can't confirm that there have been any positive tests," Brian Tobin, the ITF president, said. "We won't comment on any individual tests or results that take place throughout the year."
About 1,000 random samples were taken last year, Tobin said, adding: "Should any particular athlete ever be found in violation of the rules after full and due process, then of course he or she will be subject to the penalties proscribed.
"It's never happened before. It's funny, you sometimes get criticism for never having found a player positive, and they say, 'What's wrong with the system?' If some time you do find a player positive, they say, 'Is that bad for the sport?' If it happened, I would have thought it proves the system is sufficient. But that is only hypothetical."
Although Jennifer Capriati, the disaffected American prodigy, attended a drugs rehabilitation centre in 1994 after being arrested for being in possession of marijuana, this is the first time allegations have been made about players testing positive during a tournament.
Recreational use of cocaine is not unknown among tennis players. Borg admitted in 1992 that he had sampled the substance in the mid-1980s, Vitas Gerulataitis once had problems with cocaine, and in 1979 Yannick Noah alleged widespread recreational drug use on the tour.