"I have tested positive but I have never taken drugs and I feel 100 percent innocent," the five-times grand slam champion from Switzerland told a news conference.

Fighting back tears and with her voice cracking, Hingis read from a written statement before leaving the room without answering questions.

In an expanded version of the statement later released by her management, the 27-year-old said she found the accusation of drug-taking "so horrendous, so monstrous, that I have decided to confront it head-on by talking to the press."

The statement added: "I would personally be terrified of taking drugs. When I was informed (about the test) I was shocked and appalled."

Hingis added that she had undergone a private test that came back negative and consulted an attorney.

"The attorney and his experts discovered various inconsistencies with the urine sample that was 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."

Hingis said she had also been advised that any fight to clear her name could drag on for years.

"I have no desire to spend the next several years of my life reduced to fighting against the doping officials," she said. "I am frustrated and angry.

"I believe that I am absolutely, 100 percent innocent. The fact is that it is more and more difficult for me, physically, to keep playing at the top of the game.

"And frankly, accusations such as these don't exactly provide me with motivation to even make another attempt to do so."

She added: "And so, considering this situation, my age and the problems I have been having with my hip, I have decided to no longer play tennis on the Tour."

After rising to the top of her sport with a much-admired blend of grace and tactical astuteness, Hingis suffered a string of injuries that forced her to first hang up her racket in 2003.

She made a surprise return to the courts in 2006, proving her doubters wrong as she went on to win two more titles and end the year as world number seven.

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.

Thursday's media conference was widely expected to see the former world number one announcing her retirement -- but not in the circumstances now set out.

The WTA Tour released a brief statement from chief executive officer Larry Scott on Thursday, mainly paying tribute to Hingis's achievements on the court.

"The WTA Tour has not received any official information regarding the positive doping test result referred to... and as a result we are not in a position to comment," Scott began before going on to praise the player's "incredible touch, on-court intelligence and off-court professionalism."

Switzerland's national tennis association also highlighted Hingis's attributes as a player.

"Martina Hingis was a great player who was always a role model and a figurehead for Swiss tennis," association president Rene Stammbach said in a statement.