Another flag furore has hit the Australian Open as an apparent Novak Djokovic fan has been seen brandishing an 'ultra fascist symbol' during the men's final.

A Twitter user noticed the fan holding up a Chetnik flag during the TV broadcast of the Djokovic-Tsitsipas match.

'Why am I seeing a Chetnik flag amongst the Serbian crowd at the Tsitsipas vs Djokovic match? Are ultra fascist symbols allowed in the Australian Open now?' Sophie Mak asked.

The Chetniks were Serbian ultranationalists who committed war crimes during World War II and are widely considered to be a far-right group. 

Tennis fans took to to social media to criticise the officials for allowing the flag to be held up at Melbourne Park. 

'@AustralianOpen @TennisAustralia still hasn't removed that fascist or confiscated their flag. A total failure and a disgrace. Genuinely shameful and embarrassing,' wrote one Twitter user.

'Chetnik fascists collaborated with Nazis and murdered tens of thousands of Muslims and Croatians during World War II in efforts to create Serbian ethno state. Unsurprisingly the Australian Open security let fascist flags into stadium while cracking down on Peng Shuai shirts,' said another.

Tennis writer Ben Rothenberg called for the Australian Open to ban flags altogether if security can't stop the incidents from occurring. 

'I really think they need to make the 2024 #AusOpen a flag-free zone if their security repeatedly can't figure this stuff out. Tournament security has been pretty abysmal (though we haven't had the ~annual court invader during the men's final yet),' he wrote on twitter.

Earlier in the tournament, Djokovic's father Srbjan was warned he could face a ban from the men's final after causing outrage by being filmed next to a man who was posing with a Russian flag with Vladimir Putin's face on it.

A video posted on YouTube showed Srdjan posing alongside the flag and a sympathiser who shouts 'Long Live Russia!'

One of the men in the video clip was wearing a shirt with the 'Z' symbol - an emblem representing support for Russia's invasion of Ukraine.

The Australian Open entry rules forbid the display of any flags in support of Russia or Belarus.

Ukraine's ambassador to Australia, Vasyl Myroshnychenko, expressed his disgust at the fan behaviour.

'It's a full package. Among the Serbian flags there is a Russian flag, Putin, Z-symbol, so called Donetsk People Republic flag. It's such a disgrace,' he told the Herald Sun.