MELBOURNE - Defending champion Marat Safin today became the third high-profile men's tennis player to withdraw from the 2006 Australian Open due to injury.
The Russian said that although his knee injury was improving, he did not feel ready to play grand slam tennis.
Safin joins four-time former Open champAndre Agassi (ankle) and world No 2 Rafael Nadal of Spain (foot) on the sidelines.
And Australian world No 4 Lleyton Hewitt is currently battling a stomach virus, although he is through to the second round of the Sydney International tournament.
Safin claimed his second grand slam title when he beat Hewitt in the final at Melbourne Park last year.
But the ongoing knee problem means he has been able to play only one tournament since August.
"I am very sad that I cannot go to the Australian Open to defend my title as champion," the Russian said on his website.
"I have been working very hard and it is a lot better.
"In my heart I know I want to be at the Australian Open to try to play but I have had to listen to what Peter (coach Peter Lundgren), my team and also myself are saying that it would not be right to go to a grand slam and put so much test on my knee right now.
"I am sorry to all my Australian fans but I will be back next year."
Nadal, the reigning French Open champion, told a news conference in Barcelona overnight that he was still struggling for full fitness after injuring his left foot.
"The Australian Open is too important a tournament for me to go to without having an option to win it," said the 19-year-old Spaniard.
"The truth is that I haven't played a tournament since the final of the Madrid Masters (in October) and I've only been training at a competitive level for 10 days.
"I'm quite happy with the way I have recovered and the foot has improved quite a lot recently and I can now play almost without any pain.
"But I still need to recover full confidence in my foot and find that spark needed to play at the top level."
Nadal sustained the injury at the end of last season and was forced to withdraw from the Masters Cup in Shanghai in November.
The Australian Open starts on Monday at Melbourne Park.
