Novak Djokovic could face a fine or even prison in Serbia after his admission that he broke isolation while he had Covid last month, lawyers have said, as the Serbian prime minister warned his behaviour appeared to be “a clear breach” of the rules.

The 34-year-old Belgrade-born tennis player is chasing a record-breaking 21st grand slam victory at the Australian Open beginning on Monday, but could yet be deported by the government which is unhappy with his medical exemption from inoculation.

Djokovic on Wednesday acknowledged that he knew he had tested positive when he attended a newspaper interview and photoshoot in the Serbian capital on 18 December, saying in a statement on social media he had made an “error of judgment”.

The player also blamed “human error” by his support team for a mistake in his immigration paperwork, saying they had failed to declare that he had travelled outside Serbia – to Spain – in the two-week period before entering Australia.

Lawyers in Serbia told local reporters that breaking the country’s strict isolation rules was an offence under article 248 of the criminal code, and subject to a fine or prison sentence of up to three years – although community service was more likely.

Djokovic was freed from an immigration detention hotel in Melbourne on Monday after a judge ruled his treatment was unreasonable. The unvaccinated star is relying on a recent previous coronavirus infection for an exemption allowing him to play.

In an affidavit to the court, Djokovic said he was “tested and diagnosed” as having contracted Covid on 16 December. In his statement on Wednesday, however, he said was not notified of his positive status until the following day.

He said he was not aware he had tested positive until after a tennis event he attended in Belgrade on 17 December to present awards to children, but admitted he was aware of his status when he went to his tennis centre on 18 December for an interview and photoshoot for L’Equipe.

Lawyers in Serbia said that as a major public figure, Djokovic, who is a national hero in his home country, risked an exemplary sanction if found guilty, but suggested he should in principle be able to negotiate a community service order.

In the early stages of the pandemic, several Serbs who tested positive for Covid were handed jail sentences of up to three years up for not isolating for the obligatory 14 days, although more recent convictions have typically entailed fines of about 150,000 dinar (£1,060).

The Serbian prime minister, Ana Brnabić, said Djokovic should explain what she called a grey area. “If you’re positive you have to isolate,” Brnabić told the BBC, adding that if the player had broken the rules she would have to consult “relevant authorities”.

Brnabić said she did not know for sure “when he actually got the results”. She said while she disagreed with his stance on vaccination, Djokovic was “one of the great champions of Serbia” and she hoped he could play in the tournament.

Serbian authorities and media have largely remained fiercely supportive of the player despite the latest revelations. Earlier this week, Brnabić told a pro-government paper she was “sleeping with my mobile phone” in case she got a call about the case.

“It was really important for me to express concern over the issue. I have offered the service of the Serbian government if there is anything we can do. We have agreed to stay in communication with Australian representatives,” she said.

Mainly pro-government Serbian newspapers have not so far investigated Djokovic’s movements in Serbia while he had Covid, or questioned apparent anomalies in his test certificate. Of 18 different articles about the story on the website of the tabloid Informer on Wednesday, none questioned the player’s version of events.

In an op-ed article in the same paper, the deputy mayor of Belgrade, Goran Vesić, attacked the Australian immigration minister, Alex Hawke, who is still considering whether to exercise personal powers to again revoke the player’s visa.

“No one had heard of a certain immigration minister in Australia, Alex Hawke – but the whole world has heard of Novak Djokovic,” Vesic wrote. “Well, the world finally found out who Mr Hawke is.”

Hawke would be “anonymous had he not held his citizens in house arrest for almost two years, treating them like convicts,” Vesic continued. “The Serb opposition calls us, the ruling party, dictators – but trust me, neither the president or any one of us would ever annul a court decision.”