The Australian Open has been put in doubt after she withdrew from January's ASB Classic in Auckland, New Zealand because of ongoing health issues.
The 31-year-old former world number one has been receiving treatment for Sjogrenís syndrome.
The Australian Open, the first Grand Slam of the year, begins on January 16.
The seven-time Grand Slam winner, who is currently ranked 103 in the world, had been handed a wildcard entry to the tournament.
However, the competitionís website announced Williams had told her agent, Carlos Fleming, that she was not fit to take part despite recent exhibition match appearances.