The Serbian has repeatedly refused to reveal whether he has received a COVID-19 vaccine, raising strong doubts that he will be able to enter Australia to defend his men's singles title at Melbourne Park next month.

Organisers of the first Grand Slam of the year have warned that all players will have to be vaccinated to take part - a policy which Djokovic's father recently described as "blackmail" as he cast doubt on whether his son would play.

Djokovic fans' hopes of seeing the 34-year-old fight for a 10th Australian Open crown have been increased after he was included on the official entry list for the tournament.

The Association of Tennis Professionals Cup, a team event scheduled to be held in Sydney prior to the Australian Open, has also included the 20-time Grand Slam winner among its entries.

According to a report by News Corp Australia, Djokovic has grounds to apply for a medical exemption to allow him to compete in Australia with being inoculated.

However, Tennis Australia and Victoria's Deputy Premier James Merlino, who is also the country's Education Minister, have both denied those claims.

"All players, participants and staff at the Australian Open have to be vaccinated," a statement from Tennis Australia read.

"Any application for a medical exemption must follow strict government guidelines based on ATAGI [Australian Technical Advisory Group on Immunisation]clinical advice. 

"This is the same process that applies to any person wanting to enter Australia.

"Any suggestion that Tennis Australia is seeking loopholes within this process is simply untrue. 

"Adjudicating on medical exemptions is the domain of independent medical experts. 

"We are not in a position to influence this process and nor would we.

"The safety of everyone is always our priority as we plan for Australian Open 2022 and all lead-in events."

Merlino insisted medication exemptions were "not a loophole for privileged tennis players".

"It is a medical exemption in exceptional circumstances if you have an acute medical condition," added Merlino.

"My view and, I think, the view of all Victorians, the expectation of all Victorians is that everyone who attends the Open - players, spectators, staff, officials - [is] fully vaccinated."

While question marks continue to hang over Djokovic’s participation, American great Serena Williams has confirmed that she will not be playing at this year's Australian Open.

The 40-year-old, who is just one major away from beating Australian Margaret Court’s all-time record of 24 Grand Slam singles titles, has been struggling with a hamstring injury.

"Following the advice of my medical team, I have decided to withdraw from this year's Australian Open," said Williams.

"While this is never an easy decision to make, I am not where I need to be physically to compete.

"I will miss seeing the fans but am excited to return and compete at my highest level."

Bianca Andreescu, the Canadian who won the US Open in 2019 but has been waylaid by injuries since, will also not play in the Australian Open.

The Australian Open is scheduled to run from January 17 to 30 next year.