Serena Williams has announced that she will not defend her Australian Open title in Melbourne later this month as she has yet to return to peak fitness.

The 36-year-old returned to action against French Open champion Jelena Ostapenko in Abu Dhabi last week, just four months after giving birth to daughter Alexis Olympia.

Williams has been in full training for just a month, though, and the 23-time Grand Slam winner has decided to delay her return to the big stage until she regains her sharpness.

"After competing in Abu Dhabi I realised that, although I am super close, I'm not where I personally want to be," she said in a statement. "My coach and team always said 'only go to tournaments when you are prepared to go all the way'.

"I can compete - but I don't want to just compete, I want to do far better than that and, to do so, I will need a little more time."

Williams, eight weeks pregnant when winning her seventh Australian Open title last year, last missed the tournament in 2011.