The American refused to commit to playing at the first Grand Slam of the year at the Mubadala Tennis Exhibition in Dubai last week, though tournament director Craig Tiley reportedly remains confident she will be in action. "I appreciate the support and understanding of my fans and everyone at the Australian Open", Serena concluded her statement.
Williams had told Vogue magazine last August about her "outrageous plan" to defend her title, but the short turnaround after giving birth has proven too much for even the greatest player of her generation.
"It is better to take a bit more time, and when you come back to the competition, you are ready to be yourself - win or lose is another thing - but at least be yourself and be at the top of what you can do".
The 36-year-old was hoping to return to the court after the birth of her daughter Alexis Olympia in September.
Since then, she has just played once in Abu Dhhabi last week, where she lost to French Open champion Jelena Ostapenko.
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"Serena transcends the sport in the way she approaches all aspects of her life".
"It was never going to be good enough for her to just compete".
It is the first time since 2011 that Williams has missed the tournament.
The announcement comes after former World No 1 and four-time Australian Open finalist Andy Murray withdrew from the tournament less than two weeks ahead of its start.
There are also doubts over the fitness of Spanish world number one Rafael Nadal and Switzerland's Stan Wawrinka, who won the title in 2014.
Novak Djokovic is slated to play two exhibition events before taking a final call on his participating at the Australian Open which begins from January 15.