Russian and Belarusian flags were banned at the Australian Open earlier in the tournament after one was spotted during a match between Ukraine’s Kateryna Baindl and Russia’s Kamilla Rakhimova at Melbourne Park.

Players from Russia and Belarus are required to compete as neutrals at the Australian Open because of the war in Ukraine, a more lenient approach than most Olympic sports who have banned both countries' athletes.

Djokovic beat Russia's Andrey Rublev 6-1, 6-2, 6-4 at the Rod Laver Arena yesterday, although the match was marred by the presence of a tee-shirt with the "Z" symbol - associated with the Russian military and as nationalist propaganda insignia in the country - worn by a spectator.

The Serbian's father Srdjan Djokovic has been filmed standing with spectators carrying the Russian flag with an image of the country's authoritarian President Putin after the match.

One of the men is wearing the "Z" symbol.

It has been reported that Srdjan Djokovic was filmed proclaimiing "long live the Russians" in Serbian.

Tennis Australia did not specifically reference the incident, but warned players and their teams against posing with banned symbols.

"A small group of people displayed inappropriate flags and symbols and threatened security guards following a match on Wednesday night and were evicted," it said.

"One patron is now assisting police with unrelated matters.

"Players and their teams have been briefed and reminded of the event policy regarding flags and symbols and to avoid any situation that has the potential to disrupt.

"We continue to work closely with event security and law enforcement agencies."

Victoria Police announced that four men were evicted from Melbourne Park after the brandishing of a Russian flag outside Rod Laver Arena.

The video of Srdjan Djokovic was posted to a pro-Russian Australian YouTube account, captioned "Novak Djokovic's father makes bold political statement".

The account is run by a user identified as Simeon Boikov, and he had urged Russian supporters to protest the flag ban at Melbourne Park.

An arrest warrant was issued against Boikov earlier this week after he was accused of assaulting a 76-year-old man at a Ukraine support rally in Sydney, and he is seeking refuge at the Russian Consulate.

Serbia's relations with Russia are complex, with Belgrade balancing shared Slavic and Orthodox heritage, a reliance on Russian gas and Moscow's refusal to recognise Kosovo's independence with a bid for European Union membership and closer relations with the West.

It remains the only European country, apart from Belarus, that has refused to introduce sanctions against Russia, but has repeatedly condemned the invasion of Ukraine at the United Nations.

Serbian President Aleksandar Vučić has criticised Russian websites and social media groups for seeking to recruit its citizens to join the Wagner Group paramilitary organisation in Ukraine.

Participation in conflicts abroad is illegal for Serbians, and Wagner's founder Yevgeny Prigozhin has denied recruiting Serbs.

Djokovic is set to play American Tommy Paul in tomorrow's Australian Open semi-final, with a Russian neutral, Olympic silver medallist Karen Khachanov, playing Greece's Stefanos Tsitsipas.

Both of today's women's singles semi-finals are due to feature a Belarusian playing under a neutral flag, with Victoria Azarenka facing Kazakhstan's Elena Rybakina and Aryna Sabalenka taking on Poland's Magda Linette.