Former world number one Martina Hingis admitted she had tested positive for cocaine during Wimbledon 2007 while announcing her retirement from top-flight tennis.
However, the Swiss tennis star, a winner of five Grand Slam singles titles including Wimbledon, Thursday denied using cocaine, the Swissinfo website reported.
"I have tested positive but I have never taken drugs and I feel one hundred percent innocent," Hingis said at a news conference in Zurich.
Hingis lost in the third round at Wimbledon to Laura Granville, 6-4, 6-2.
"The reason I have come out with this is because I do not want to have a fight with anti-doping authorities," she said.
"Because of my age and my health problems I have also decided to retire from professional tennis," said the 27-year-old, fighting back tears.
Hingis said she was accused by "an outsource testing company" of taking cocaine during Wimbledon. She said she was "shocked and appalled" when notified that her urine sample came back positive after the loss to Granville.
Hingis also said she hired an attorney who found "various inconsistencies" with the urine sample taken during Wimbledon.
"He is also convinced that the doping officials mishandled the process and would not be able to prove that the urine that was tested for cocaine actually came from me," she said.
Hingis said it could take years to fight her case and decided it was time to retire.
The former teenage sensation took over at the top of women's tennis in 1997 when she won three of the four Grand Slams, only missing out at Roland Garros.
She managed to stay in the top spot for 209 weeks. Only Steffi Graf, Martina Navratilova and Chris Evert have a better record than the 27-year-old.
The Czech-born Swiss, who won many fans for her graceful and tactical style of tennis, first announced her retirement in 2003 after failing to overcome a series of ankle injuries.
She made a surprise return to the courts in 2006, proving her doubters wrong as she went on to win two more titles.
A further final title followed in Tokyo this year before her injury problems returned. In October, Hingis announced an early end to her season, citing hip problems.
"Martina Hingis was a great player who was always a role model and a figurehead for Swiss tennis," Rene Stammbach, president of the Swiss Tennis Association, said in a statement.
"We regret very much that Martina is ending her career faced with these recriminations."