Police are at the lawyers' office of Novak Djokovic as the Australian government continues its bid to deport the tennis star.
The Serbian world number one earlier won a court battle challenging the cancellation of his visa.
Judge Anthony Kelly ordered the Australian Government to pay legal costs and release Djokovic from detention within half an hour.
Serbian press is reporting Djokovic's father believes the 34-year-old was arrested after winning the appeal, although this appears not yet to be the case.
His brother Djordje confirmed the reigning Australian Open champion was still in danger of being kicked out of the country, reports the Mirror.
He told the Sport Klub broadcaster: "What we can do is to let this be known all over social media – they want to capture and lock up Novak again. We're currently consulting with PRs about next steps.
"He is at the moment with his lawyers in the room they were during the hearing, thinking about options."
Djokovic was held in a quarantine hotel over the weekend waiting for the outcome of his appeal, which was heard on Monday.
Despite the judge's ruling, Australian immigration officials still have the power to quash his visa if they deem it in the public interest.
If Djokovic is deported, it could mean he is ineligible to play at the Australian Open for three years.
Eyewitness reports confirmed a significant police presence at his lawyers' office in Melbourne.
Djokovic flew in to Australia last week hoping to defend his title at the tournament, which begins later this month.
He is bidding to win his 21st Grand Slam – a haul that would take him past fellow tennis stars Rafael Nadal and Roger Federer.
Djokovic, who is unvaccinated against Covid-19, was granted a medical exemption to enter the country and play at Melbourne Park.
But his visa was cancelled by the Border Force on arrival and he was instructed to leave the country.
Djokovic and his lawyers appealed the decision, and he was kept in a detention centre for refugees over the weekend ahead of the appeal being heard on Monday.
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