The 22-year-old announced on Friday that she would not compete again this year, after a run of disappointing results.

And the Swiss gave no indication when she would return to the women's circuit.

Hingis, who returned to action in August following ankle surgery, broke the shock news at a conference called to explain her absence from next week's Swisscom Challenge event.

"I will not play any more tournaments this year. I need to free my mind," she said, adding her recent performances in Moscow and Germany had been below her expectations.

Next week, Hingis will slip out of the world's top 10 for the first time in six years.

She rose to fame in 1996 at Wimbledon, where she became the All England Club's youngest ever champion at 15 by taking the women's doubles title with Helena Sukova.

Hingis followed that feat by becoming the youngest Grand Slam singles winner for more than a century when she won the Australian Open the following year.

Jeered in Paris

And she added singles titles at Wimbledon and the US Open en route to an 80-week reign as the world's number one player.

But things began to turn sour for Hingis in 1999, when she was jeered from the court at the French Open after defeat by Steffi Graf.

In May, 2002, she underwent surgery on her left ankle.

And Hingis has not found her best form since returning from that injury in August.