He wrote: "It's quite demoralising that when you get on the court it's not at the level you need it to be to compete at this level".
With his participation at the Australian Open in risk, the Serb confirmed on Facebook and on his website what Michal Samulski, member of International Tennis Writers Association, had written on Twitter.
The 36-year-old, who won last year's trophy while eight months pregnant, has played just one match since the birth of daughter Alexis Olympia.
Former world No. 1 Novak Djokovic will travel to Australia to test his long-standing elbow injury before deciding whether or not to play in the Australian Open.
"After competing in Abu Dhabi I realized that although I am super close, I'm not where I personally want to be", Williams said in a statement.
Since Wimbledon last season, Novak Djokovic hasn't played. In terms of total years, it was the oldest Grand Slam women's final in the Open era with the Williams sisters combining for 71 years, 11 months.
The Serbian is now due to contest both the Tie Break Tens at Melbourne Park on January 10, and the Kooyong Classic, an invitational competition staged at the former home of the Australian Open.
"Serena transcends the sport in the way she approaches all aspects of her life and consistently gives her all in everything she does".
"I've been in constant contact with Serena and her team and know this is why she has pushed it and pushed it until the eleventh hour to make her final decision".
Tiley also expressed his admiration for Serena's efforts to return to the game she loves.
"I appreciate the support and understanding of my fans and everyone at the Australian Open".
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