WORLD tennis number one Steffi Graf described 16-year-old Martina Hingis as a breath of fresh air and said she was not upset by the prospect of losing her top ranking to her.

"I didn't think Martina would become so good," Graf told the German magazine Spoils Live yesterday. "Martina exudes a freshness that can only be good for the tour."

Graf faces a four-week lay-off with a knee injury and will be unable to defend two titles in the United States.

This means Hingis, whose win at last month's Australian Open made her the youngest singles champion at a major championship since 15-year-old Lottie Dod won Wimbledon in 1887, will almost certainly take over the number one ranking which Graf has held for a record 373 weeks in succession.

But Graf, holder of 21 Grand Slam titles, insisted she was not worried. "My sporting satisfaction has nothing to do with world rankings," she said. "I'm more than happy if the interest moves away from me for a bit, especially after the strains of the last few months (when Graf's father was on trial for tax evasion)."

Graf, however, said she was disappointed by the failure of other players to challenge herself and Hingis more strongly. "There are some who could get a great deal more out of themselves," she said. "Monica (Seles) could if she wanted to. But I don't think she really wants to any more."

In the interview, Graf affirmed her innocence in the tax evasion affair for which her father, who managed her multi-million dollar income, has been sentenced to three years and nine months in jail.

Prosecutors have said they may still press charges against Graf herself, whose signature was on the tax returns. "When I heard that I was also supposed to be guilty in the tax affair, it really upset and affected me," she said.

"I knew what I had done and that I was free of any guilt, only I was unable to explain it to anyone. I would have liked to tell every single person: `I'm innocent'."