Reigning women's Australian Open champion Justine Henin-Hardenne withdrew from this year's Grand Slam tournament on Saturday because of a knee injury.

The Belgian battled a mystery illness for most of last year, but still managed to win a gold medal at the Athens Olympics [Images] in August and was hoping to be fit enough to defend her title in Melbourne later this month.

However, the world number eight was a late withdrawal from the January 9-15 Sydney International tournament, a warm-up event she won last year.

"It is disappointing because I was so happy to be back and playing," Henin-Hardenne told reporters in Sydney:

"The rest of me is feeling good after last year which was so difficult.

"I have to be careful and smart but it is hard to accept this decision. I have to go home (Belgium) and get rest."

Australian Open spokesman John Lindsay verified her withdrawal from the grand slam, telling Reuters:

"I've just had confirmation on Justine Henin-Hardenne. She has a minor fracture of the femoral condyle of the right knee, which she did on December 28th in Florida [Images].

"She had a scan today but still has problems so she is pulling out of the Sydney tournament and the Australian Open.

"She's going to rest for four to six weeks."

Last year's losing Open finalist Kim Clijsters [Images], also of Belgium, pulled out of the tournament on Friday because of a wrist complaint.

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