Nick Kyrgios is a doubt to take part at the Australian Open after testing positive for COVID-19.

The Australian star withdrew from the Sydney Tennis Classic hours before he was due to face Fabio Fognini.

The 26-year-old had already pulled out of the Melbourne Summer Set last week after struggling with an unknown illness that affected his asthma.

He was tested for coronavirus but all had come back negative until Monday.

With the first grand slam of 2022 just one week away, Kyrgios hopes he will recover in time to enter the draw.

"Hey everyone, I just want to be open and transparent with everyone, the reason I have had to pull out of Sydney is because I tested positive for Covid," he wrote on Instagram.

"I am feeling healthy at the moment with no symptoms. I wish everyone all the best and to stay safe where you can.

"If all goes well I will see you all at the Australian Open."

Kyrgios has not played a singles match since losing to Stefanos Tsitsipas at the Laver Cup last September and has dropped to 114 in the world rankings.

The former world number 13, who lost a thrilling five-set match with Dominic Thiem in the round of 32 in Melbourne last year, has only once gone as far as the quarter-finals at his home grand slam.

He reached the last eight in 2015, where he lost in straight sets to beaten finalist Andy Murray.

Rafael Nadal joked that he would rather Novak Djokovic does not play at the upcoming Australian Open after the world number one won his appeal to remain in the country.

Djokovic was left fighting for the right to compete at the opening grand slam of the year, a tournament he has won nine times, after authorities cancelled his visa last week.

A medical exemption was expected to allow the Serbian to enter the country, regardless of his vaccination status, which he has yet to formally disclose.

But the Australian Border Force declared Djokovic had been ordered to fly out of the country on Thursday, sparking a challenge to that decision by the tennis star's legal team.

After both sides had presented their cases, Djokovic was handed an Australian Open lifeline on Monday when defeating a deportation order brought by Australia's government

Judge Anthony Kelly ruled at Melbourne Circuit Court that Djokovic's visa cancellation order should be "quashed" immediately.

There may yet be another twist in the saga, though, as Australia's immigration minister Alex Hawke could still cancel the 34-year-old's visa on new grounds.

Djokovic now appears far more likely to defend his Australian Open crown than he did over the weekend, however, as he goes in search of a 21st major title.

While that will inevitably make Nadal's chances of success at Melbourne Park a whole lot tougher, the Spaniard said the decision to grant Djokovic's freedom must be respected.

"Whether or not I agree with Djokovic on some things, justice has spoken and has said that he has the right to participate in the Australian Open," he told Onda Cero.

"I think it is the fairest decision to do so, if it has been resolved that way. I wish him the best of luck.

"But on a personal level, I'd much rather he didn't play!"

Nadal described Djokovic's COVID-19 vaccination controversy "a circus" and reiterated that the vaccine "is the way to stop this pandemic and disaster".

The 35-year-old ramped up his preparations for the Australian Open by winning last week's Melbourne Summer Set without dropping a single set.

That was Nadal's first tournament in five months due to injury and means he has won at least one ATP Tour trophy in every season since 2004 onwards.

He is level with Djokovic and fellow great Roger Federer on 20 grand slam titles, with the trio locked in a race to finish with the most majors.

Novak Djokovic has sensationally been handed an Australian Open lifeline by a Melbourne court.

The men's tennis world number one secured his freedom, defeating a deportation order brought by Australia's government.

The Serbian secured an injunction against immediate deportation on Thursday and spent the weekend at a detention hotel.

Ahead of the Australian Open, where he has won the men's singles title a record nine times, including last year, Djokovic arrived in the country with what he insisted were the correct documents.

Yet Australian Border Force officials cancelled his visa application, stating Djokovic had "failed to provide appropriate evidence to meet the entry requirements to Australia".

Lawyers for the 34-year-old stated he was granted a temporary activity visa on November 18.

The legal team said he was granted a medical exemption for the first grand slam of the year after a COVID-19 positive test on December 16, and was later given the go-ahead by Australia's Department of Home Affairs to travel.

However, lawyers for the government issued their own court filing on Sunday, disputing Djokovic's right to come to Australia.

"There is no suggestion that the applicant had 'acute major medical illness' in December 2021," said the government filing. "All he has said is that he tested positive for COVID-19. This is not the same."

The issue has become a political hot topic in Australia, with Djokovic's stance on COVID-19 matters rankling with many, particularly in the state of Victoria, who have faced hard lockdowns during the pandemic.

The case was listed as Novak Djokovic v Minister for Home Affairs. That is Karen Andrews; however, the matter has been one in which prime minister Scott Morrison has also become a central figure, insisting when Djokovic's visa was revoked: "Rules are rules, especially when it comes to our borders. No one is above these rules."

Djokovic has declined to confirm his vaccination status, but by requiring an exemption to compete at Melbourne Park it has been widely assumed he has not been jabbed. The government filing on Sunday stated it was "common ground that the applicant is unvaccinated".

His case was heard at Melbourne's Federal Circuit Court on Monday, with Judge Anthony Kelly ruling that the Serbian's visa cancellation order is "quashed" immediately.

This means Djokovic's visa is now valid and he can enter Australia ahead of the Australian Open getting underway in a week's time.

Tournament director Craig Tiley had said ahead of the hearing that he hoped Djokovic would be cleared to play and defend his title.

The drawn-out saga may not be entirely over just yet, however, as government lawyer Chris Tran indicated Australia's immigration minister – who has exceptional powers – may consider cancelling Djokovic's visa again.

Novak Djokovic has sensationally been handed an Australian Open lifeline by a Melbourne court.

Novak Djokovic faced a crunch day as his lawyers fought to win his freedom to play at the Australian Open – but the failure of a live court stream left the world in the dark about what was being disclosed.

Djokovic's case went before Melbourne's Federal Circuit Court on Monday, with the world number one attempting to defeat a deportation order brought by Australia's federal government.

Video footage of proceedings was promised by court officials, with huge global interest in the case, but at the scheduled hearing start time of 10am the website platform had crashed.

With the stream unavailable, the hearing was initially said by court officials to have been delayed, before word came through shortly after 10.30am in Melbourne that it had begun.

Serbian superstar Djokovic secured an injunction against immediate deportation on Thursday and spent the weekend at a detention hotel.

Ahead of the Australian Open, where he has won the men's singles title a record nine times, including last year, Djokovic arrived in the country with what he insisted were the correct documents.

Yet Australian Border Force officials cancelled his visa application, stating Djokovic had "failed to provide appropriate evidence to meet the entry requirements to Australia".

Lawyers for the 34-year-old have since stated the Serbian was granted a temporary activity visa on November 18. Djokovic's legal team said he was granted a medical exemption for the first grand slam of the year after a COVID-19 positive test on December 16, and that he was later given the go-ahead by Australia's Department of Home Affairs to travel.

However, lawyers for the federal government submitted their own court filing on Sunday, disputing Djokovic's right to come to Australia.

"There is no suggestion that the applicant had 'acute major medical illness' in December 2021," said the government filing. "All he has said is that he tested positive for COVID-19. This is not the same."

The government document also stated that, should the hearing ruling go in Djokovic's favour, it must be expressly stated that he could not be re-detained or have his visa cancelled once again. Otherwise, he could be denied entry to the country once more.

The issue has become a political hot topic in Australia, with Djokovic's stance on COVID-19 matters rankling with many, particularly in the state of Victoria, who have faced hard lockdowns during the pandemic.

The case was listed as Novak Djokovic v Minister for Home Affairs. That minister is Karen Andrews; however, the matter has been onee in which prime minister Scott Morrison has also become a central figure, insisting when Djokovic's visa was revoked: "Rules are rules, especially when it comes to our borders. No one is above these rules."

Djokovic has declined to confirm his vaccination status, but by requiring an exemption to compete at Melbourne Park it has been widely assumed he has not been jabbed. The government filing on Sunday stated it was "common ground that the applicant is unvaccinated".

Judge Anthony Kelly turned down a government request to delay the hearing by two days until Wednesday.

Australian Open tournament director Craig Tiley said ahead of the hearing that he hoped Djokovic would be cleared to play.

The Australian government has suggested it will block Novak Djokovic's entry into the country even if the world number one wins his appeal against their decision to cancel his visa.

Djokovic, who has not revealed his COVID-19 vaccination status, seemed set to compete in the Australian Open under a medical exemption.

Yet he is currently in an immigration detention hotel awaiting a hearing on Monday, after Australian border forces refused to allow him entry.

Court papers filed by Djokovic's representatives on Saturday stated that the 34-year-old had been given the medical exemption after testing positive for COVID-19 on December 16. 

The Serbian's lawyers also claimed they had an assessment from the Australian Department of Home Affairs which stated that his responses on his Traveller Declaration form met the requirements for quarantine-free travel into Australia.

Australia's government responded by filing court papers of its own on Sunday.

The 13-page document not only challenged the claim that Djokovic had COVID-19 last month, but also indicated the government would still refuse the nine-time Australian Open champion entry into the nation even if the hearing was decided in the player's favour.

The document claimed the government "had not represented to the applicant that his so-called 'medical exemption' would be accepted."

Australia's government also argued that: "There is no suggestion that the applicant had 'acute major medical illness' in December 2021. All he has said is that he tested positive for COVID-19.

"That is not the same. Thus the ATAGI Vaccination Advice uses different terms, such as mere "past infection" and also "symptomatic infection"."

The document goes on to conclude that, should the hearing be ruled in Djokovic's favour, it must be expressly stated that he could not be re-detained or have his visa cancelled once again.

"If this Court were to make orders in the applicant's [Djokovic] favour, it would then be for the respondent [Australian government] to administer the Act in accordance with law.

"That may involve the delegate deciding whether to make another cancellation decision, but there are also other powers in the Act, as the Court would be aware. Or, indeed, no power may be exercised.

"It is sufficient for the Court to quash the decision. From the time those orders are made, the respondent will act on the basis that the applicant's visa has not been cancelled.

"If the Court makes an additional orders for immediate release of the applicant, notwithstanding the above, the respondent submits that the Court should make it expressly clear that that order does not purport to (nor could it) prevent the respondent or any officer of the Commonwealth from exercising any power to detain that might be available to him or her despite the quashing of the delegate's cancellation decision.

"An order for immediate release does not prevent re-detention if there is power to detain."

Andy Murray believes Novak Djokovic's situation ahead of the Australian Open does not reflect well on anyone involved, nor the game of tennis in general.

Djokovic is currently in immigration detention at the Park Hotel in Melbourne.

The world number one, who has not revealed his COVID-19 vaccination status, received a medical exemption to feature in the Australian Open, which begins on January 17. He is the reigning champion and has won the tournament nine times.

All competitors at Melbourne Park must either be vaccinated or have a valid medical reason not to have had the vaccine. Australia, and Melbourne in particular, has had strict restrictions in place throughout the pandemic.

However, Djokovic's visa application was rejected by Australian border force officials. The Serbian star will now await the outcome of a hearing, set to take place on Monday, to determine whether he will be allowed to compete or be deported, with the Australian government losing an appeal to delay the hearing.

Murray, a five-time Australian Open finalist, cannot see how the situation looks good for anybody.

"I think everyone is shocked by it to be honest," former world number one Murray, who is preparing himself for the season's first grand slam, told reporters, as quoted by Australian publication The Age.

"I'm going to say two things on it just now. The first thing is that I hope that Novak is OK. I know him well, and I've always had a good relationship with him and I hope that he's OK.

"The second thing I'll say on it, is it's really not good for tennis at all, and I don't think it's good for anyone involved."

Four of Murray's five defeats in Australian Open finals came to Djokovic, who the Scot has not had contact with.

"[I need to] wait and hear exactly what the situation is before commenting on it further, because again I don't think it's fair because some of it is speculation," Murray said.

"Some stuff has come out that really doesn't look good, either. I want to hear all the facts first before giving all of my thoughts on it."

Djokovic's lawyers, in their appeal document sent to the court, disclosed that the 34-year-old had tested positive for COVID-19 in December, and it was under these grounds that they sought a medical exemption.

Rafael Nadal said this week that Djokovic could have made life easier for himself by getting vaccinated, or disclosing his vaccine status, and Murray echoed those sentiments.

"It's not for [Nadal] to say what the right thing to do is, but to listen to the experts on those subjects, and I feel the same," Murray added.

"I can accept that young healthy athletes, if you contract coronavirus, are probably going to be OK. But I trust what I'm getting told by the scientists and the doctors.

"It's not about listening to what politicians or government are telling me to do, it's more listening to the doctors and the scientists, and the people that really know about that stuff."

Ash Barty defeated Elena Rybakina in straight sets to claim the Adelaide International title, while Simona Halep clinched silverware in Melbourne.

World number one and heavy favourite Barty prevailed 6-3 6-2 against Rybakina to claim the Adelaide title for a second time in three seasons.

The 25-year-old recovered from 40-15 down in the seventh game and went on to immediately earn the only break of the opening set.

Barty did not look back as she held throughout the second set, meaning she went 35 consecutive games without losing serve to conclude the tournament.

After securing a 14th WTA singles title in a little over an hour, Barty now turns focus to next week's Sydney Tennis Classic ahead of beginning her Australian Open campaign.

"I feel good leading up to an Australian Open like I have every year," Barty, who hit 17 winners to 13 unforced errors, said after seeing off Rybakina. 

"Each and every preparation is unique. We take it for what comes and what it is, move on, try and do the best that we can in every opportunity.

"It has absolutely no effect on the way that I prepare or the way I'm thinking leading forward just because it's a Grand Slam. It doesn't change for us."

Halep, one of Barty's likely rivals for the Australian Open crown, also made a bright start to the year by overcoming Veronika Kudermetova in the Melbourne Summer Set 1 final.

The number two seed, who is aiming to put last year's injury-ravaged and trophyless season behind her, came out on top 6-2 6-3.

She recovered from an early break down in the first set and again in the second to make it 23 career titles, and a first since the 2020 Italian Open.

It could easily have been a different story, however, as Kudermetova had three break points to move 3-0 ahead in the second set, but the Russian could not take full advantage.

Amanda Anisimova defeated Aliaksandra Sasnovich at the Melbourne Summer Set 2 final to claim the first WTA title of the season, and her second overall.

Belarusian qualifier Sasnovich hit back in style to take the second set 6-1 after losing the opener 7-5, but Anisimova recovered from a break down to edge the deciding set 6-4.

In doing so, Anisimova became the first American to win a title on Australian soil since Sofia Kenin's Australian Open triumph in 2020.

Novak Djokovic's court appeal will take place on Monday after Australian Department of Home Affairs lawyers lost a bid to delay the timing of the case.

Home Affairs' lawyers applied to the Federation Circuit Court to re-schedule the case by two days from Monday to Wednesday but the application was dismissed by Judge Anthony Kelly.

Delaying the appeal until Wednesday would have been after Tennis Australia's stated deadline for inclusion in the upcoming Australian Open, due to begin on January 17.

Djokovic and his lawyers filed court documents on Saturday stated that the Serbian was granted a temporary activity visa on November 18, having been detained upon arrival in Melbourne.

The world number one's legal team are battling for him to be freed in order to prepare for and participate in the Australian Open in Melbourne.

Australian Border Force officials cancelled his visa application on Thursday, stating Djokovic had "failed to provide appropriate evidence to meet the entry requirements to Australia".

Djokovic had been granted a medical exemption by organisers of the first grand slam of the year, but his fate now hangs in the balance.

Novak Djokovic tested positive for COVID-19 in December and was later given the go-ahead by Australia's Department of Home Affairs to travel to Melbourne, his lawyers said on Saturday.

Novak Djokovic will be "p***ed off" and more determined than ever to win the Australian Open if he is freed from detention on Monday, according to Nick Kyrgios.

The nine-time champion at Melbourne Park had his visa revoked when he arrived in Australia this week, with Border Force officials determining he had "failed to provide appropriate evidence to meet the entry requirements".

He secured an injunction to avoid immediate deportation on Thursday and is spending the weekend at the Park Hotel, also home to refugees and asylum seekers, before his case is heard in court on Monday.

His lawyers have filed a detailed response and called for Djokovic to be liberated, also revealing the 34-year-old Serbian tested positive for COVID-19 on December 16 and has made a full recovery.

Djokovic has a startling 82-8 win-loss career record at the Australian Open and has earned $21,775,855 (US dollars) for his endeavours at the first grand slam of the tennis season.

Should he be cleared to play this time, and successfully defend his title, it would make him the outright leader for men's grand slam titles with 21, nudging him ahead of Rafael Nadal, who is also set to compete, and Roger Federer, who is absent.

Kyrgios has been a fierce critic of Djokovic in the past, but the Australian firebrand this week said the handling of the Belgrade superstar's case had been "really bad" and those taking satisfaction from his situation should "do better".

Having aired those views on social media, Kyrgios expanded on his thoughts in a news conference on Saturday, saying: "For the sport, we need him here.

"I'm feeling for him now, it's not really humane what’s going on. If he's allowed to play the Australian Open, I don't want any bar of him. I reckon he's going to be p***ed off.

"He's going to be very determined to play well and stick it to everyone. And I don't want any bar of that Novak."

Kyrgios claimed media coverage of his comments about Djokovic has "divided us", stating his past remarks have been "blown out of proportion".

In January 2021, Kyrgios described Djokovic as "a tool" after reports he was seeking privileged quarantine restrictions ahead of last year's Australian Open.

Speaking to the No Challenges Remain podcast in 2019, Kyrgios said of Djokovic: "I just feel like he has a sick obsession with wanting to be liked. He just wants to be like Roger [Federer]."

There has been obvious animosity in the past, but this time around Kyrgios is siding with Djokovic. He wants there to be a greater respect shown by Australia towards the world number one.

"I feel he's helped us as well. Like during the bushfires, he was supportive, he was helping us out," Kyrgios said.

"I feel like I could use this as a publicity stunt. I could just agree with the general person and say, 'Yeah, this isn't good', and use it. But I don't think that's right."

Novak Djokovic tested positive for COVID-19 in December and was later given the go-ahead by Australia's Department of Home Affairs to travel to Melbourne, his lawyers said on Saturday.

The men's tennis world number one is being detained at the Park Hotel in Melbourne ahead of a court hearing on Monday that should determine whether he is allowed to stay in Australia.

The Australian Open begins on January 17 and Djokovic's legal team are battling for him to be freed in order to prepare for and participate in the tournament.

Australian Border Force officials cancelled his visa application on Thursday, stating Djokovic had "failed to provide appropriate evidence to meet the entry requirements to Australia".

Djokovic had been granted a medical exemption by organisers of the first grand slam of the year, but his fate now hangs in the balance.

His lawyers filed a detailed submission to the Federal Circuit and Family Court of Australia on Saturday, in which it was stated that Djokovic was granted a temporary activity visa on November 18.

This did not contain any conditions regarding his vaccination status, lawyers for Djokovic said, adding that the Serbian then tested positive for coronavirus, after a PCR check, on December 16. This was confirmed by the Institute of Public Health of Serbia, the 34-year-old's lawyers said.

Subsequently, having recovered from COVID-19, Djokovic was informed he was eligible to play the first grand slam of 2022 by Tennis Australia officials.

According to details filed by his lawyers, Djokovic received confirmation on December 30 from Tennis Australia's chief medical officer that he had been awarded a medical exemption to compete, on the basis he had recently recovered from the virus.

"Mr Djokovic had also received, on 01 January 2022, a document from the Department of Home Affairs in regard to his Australian Travel Declaration," his lawyers said.

This document, according to his representatives, stated that Djokovic was informed "[his] responses indicate[d] that [he met] the requirements for a quarantine-free arrival into Australia where permitted by the jurisdiction of your arrival".

If cleared to leave his hotel and compete in the Australian Open, Djokovic will be seeking a 10th title at Melbourne Park and a 21st grand slam. He currently shares the men's record of 20 major titles with Roger Federer and Rafael Nadal.

Naomi Osaka will be hoping to be fit for the Australian Open after the reigning champion withdrew from the Melbourne Summer Set 1.

Osaka, who won the most recent of her four grand slam titles last year at Melbourne Park, has looked in fine form this week in her first appearances since returning from the break she took from tennis last year.

The top seed beat Alize Cornet, Maryna Zanevska and Andrea Petkovic en route to the semi-finals, but could not compete against Veronika Kudermetova on Saturday, citing an abdominal injury.

Osaka explained that her body had taken a hit from playing such intense matches in consecutive days, and she instead is looking to rest and recover ahead of the first grand slam of the season, which starts on January 17.

"Sad to withdraw due to injury from my match today, my body got a shock from playing back to back intense matches after the break I took," Osaka tweeted.

"Thank you for all the love this past week [Red heart] I’ll try to rest up and I’ll see you soon!"

Osaka's injury has prevented what looked to be an enticing showdown with Simona Halep, who guaranteed a place in a WTA Tour singles final for a 13th successive season by beating Chinese teenager Zheng Qinwen 6-3 6-2.

Halep's first final came in 2010 and she has taken just a week to get back into her stride after an injury-ravaged 2021 season.

The Romanian, a two-time grand slam champion, went into the week ranked at world number 20, her lowest position at the start of a season since 2013.

However, she has now reached at least the semi-final stage in three successive tournaments, and she will fancy her chances against third seed Kudermetova, who is into her third singles final.

Novak Djokovic thanked the supporters campaigning for him to be allowed to play at the Australian Open as he spoke out for the first time since being detained in Melbourne.

The ATP world number one will spend the weekend in a hotel that also houses refugees and asylum seekers, some of whom have been waiting years for the chance of freedom.

A court hearing on Monday should determine Djokovic's fate after Border Force officials cancelled his visa application, stating the 34-year-old had "failed to provide appropriate evidence to meet the entry requirements to Australia".

Djokovic seemed all set to play after he was granted a medical exemption by organisers of the first grand slam of the year, but his fate now hangs in the balance. An injunction secured by his legal team has allowed him to remain in the country for now, albeit in detention.

The Serbian superstar wrote on Instagram: "Thank you to people around the world for your continuous support. I can feel it and it is greatly appreciated."

That came after a message from Djokovic to mark Orthodox Christmas on Friday, as he wrote: "Peace of God. Christ was born. Merry Christmas. May God's love strengthen and fulfil you."

The Australian Open begins on January 17 and this is just about the worst possible preparation for the 20-time major winner, even if he is given permission to remain in Australia at Monday's hearing.

There was an outcry from many Melburnians when Djokovic announced on Tuesday that he was on his way to the tournament with an exemption pass.

A small number have since protested that Djokovic should be liberated, while he has found some support on social media and extensive backing from his homeland, with Serbian president Aleksandar Vucic accusing Australian authorities of "harassment of the best tennis player in the world", pledging to "fight for Novak Djokovic, for justice and truth".

Djokovic is a record nine-time champion at Melbourne Park, but there is said to be a strong feeling locally that he should have to show proof of being vaccinated against COVID-19, given the efforts residents have gone to and the stringent restrictions imposed on them during the pandemic to date.

Australian Open officials have claimed "rigorous" checks were put in place to assess the veracity of any claim for an exemption.

One theory that has been widely suggested is Djokovic, who has spoken out about vaccine matters in the past, may have been awarded the exemption on the basis he had a positive test for COVID-19 in the past six months. He has not publicly confirmed he has recently had the virus.

However, reports from Australia have stated federal government officials instructed Tennis Australia in recent months that experiencing a recent case of coronavirus was not an adequate explanation for a player not being fully vaccinated.

Djokovic's wife, Jelena, issued a statement in support of her husband, posting on Instagram: "We wish we are all together today, but my consolation is that at least we are healthy. And we will grow from this experience.

"Thank you dear people, all around the world for using your voice to send love to my husband. I am taking a deep breath to calm down and find gratitude (and understanding) in this moment for all that is happening.

"The only law that we should all respect across every single border is love and respect for another human being. Love and forgiveness is never a mistake but a powerful force."

Australian authorities, all the way up to prime minister Scott Morrison, have contended their border laws are there for a good reason, with Monday promising to be a seismic day in the capital of Victoria.

Novak Djokovic has been warned by Boris Becker that his "stubbornness" could prevent him being remembered as the greatest tennis player that ever lived.

World number one Djokovic, who has not declared his COVID-19 vaccination status, seemed set to play in this month's Australian Open after he was granted a medical exemption by tournament organisers.

That was required for any player who has not been fully vaccinated. One theory that has been widely suggested is that Djokovic may have been entitled to an exemption after a positive test for COVID-19 in the past six months, although he has not confirmed he has recently had the virus.

However, Djokovic is now set to spend the weekend in a Melbourne detention hotel in which refugees and asylum seekers are also being kept, after Australian Border Force's decision to cancel his visa application.

A court hearing on Monday should provide a resolution to the saga, with Djokovic's legal team set to battle for his right to enter the country and play in the season's first grand slam, at which he would be bidding to win a record 21st men's singles major title. The Australian Open gets under way on January 17.

Becker coached Djokovic for three seasons, from 2014 to 2016, and told the Daily Mail the 34-year-old Serbian is "making a big mistake in not getting vaccinated".

The German said the decision "is one that threatens what remains of his career and his chance to cement himself as the greatest player of all time".

Becker, a six-time grand slam winner, said: "The same incredible determination which I saw win so many close matches can be a vulnerability with his stubbornness.

"It is not just about Australia. The fact is that we are living in a different world and he is going to find it very hard to live the life of a professional tennis player travelling around without the vaccination.

"Maybe one day we will get back to a more normal situation, but at 34 he does not have much time left to pursue his goals."

There have been protests on the streets of Melbourne and Belgrade, with arrests made by police in the Victorian capital, while Djokovic found some support from within the tennis fraternity on Friday, as American John Isner backed his case.

Isner wrote on Twitter: "What Novak is going through right now is not right. There’s no justification for the treatment he’s receiving. He followed the rules, was allowed to enter Australia, and now he’s being detained against his own will. This is such a shame. #IStandWithNovak".

Nick Kyrgios, who has had his run-ins with Djokovic in the past, labelled Australia's handling of the situation "really bad", while former world number one Andy Roddick also appears to be in Djokovic's corner.

Yet Australia's home affairs minister Karen Andrews rejected any idea that Djokovic was being "held captive".

Andrews told the ABC: "Can I say, firstly, that Mr Djokovic is not being held captive in Australia. He is free to leave at any time that he chooses to do so and Border Force will actually facilitate that.

"Yes, there was a visa issued – that is actually not the issue. It is the second part of that process, which is the specific entry requirements to be able to cross Australia's border and to enter Australia lawfully."

She said Djokovic was not the only tennis case that was under investigation by Australian authorities. A player and an official are reported to be under scrutiny.

"I'm aware of investigations in relation to two individuals by the Australian Border Force," Andrews said. "They're going through their processes of investigation.

"And at some time, they will brief me, but all I can absolutely assure you and the rest of Australia of is that the Australian Border Force will take absolutely the appropriate action."

The Professional Tennis Players Association (PTPA) has issued an update on Novak Djokovic, expressing their view that he should be allowed to compete at the Australian Open with an approved medical exemption.

World number one Djokovic, who has not declared his COVID-19 vaccination status, seemed set to play in the year's opening major, which he has won nine times previously, after he confirmed he had received a medical exemption to compete.

Protocols in Australia require proof that players have been vaccinated or have a medical exemption to compete at Melbourne Park.

Tournament director Craig Tiley insisted that the 20-time major champion had not been given a "special favour" to play in the tournament, though the decision faced immediate and widespread backlash and on Wednesday, Djokovic's visa application was cancelled.

However, the Serbian's legal team filed for a judicial review, with the case to be heard by Federal Circuit Court Judge Anthony Kelly on Monday at 10am local time in Melbourne.

Djokovic is now hauled up in a Melbourne hotel, and cannot be deported until the hearing has taken place unless he leaves the country of his own volition.

Protestors have also appeared outside of the hotel where Djokovic has been transferred, while Nick Kyrgios has expressed his displeasure at the way the situation has been handled.

The matter has also drawn criticism from Serbia's president Aleksandar Vucic, who labelled Australia's treatment of the nation's superstar as "harassment."

On Friday, the PTPA - which was founded by Djokovic and Canadian player Vasek Pospisil in 2020 - issued an update on the situation.

The PTPA has been diligently monitoring the detainment of professional tennis player Novak Djokovic by the Australian Government.

"The PTPA has been in close contact with Mr Djokovic, his family and legal counsel, government officials and Australian Open leadership," a statement read.

"Mr Djokovic has verified his well-being to us. He has also requested that we allow him to personally share the facts of his detainment in his own words, and in his own time.

"With the utmost respect for all personal views on vaccinations, vaccinated athletes and unvaccinated athletes (with an approved medical exemption) should both be afforded the freedom to compete. We will continue to support and advocate for our members, and all players, in a manner that is acceptable to them."

The statement concluded with: "We will continue to monitor his health, safety and well-being. We look forward to his time back on the court."