The national flags of Russia and Belarus are banned at the Grand Slam, as well as the former flags of the Russian Empire - mostly sporting black-and-yellow characteristics.

As well as these flags, the "Z" symbol - associated with the Russian military and as nationalist propaganda insignia in the country - has also been banned.

On Twitter, the 34-year-old Dolgopolov asked for action to be taken by organisers following the match involved Rublev, winner of an Olympic gold medal at the re-arranged Games in Tokyo, representing the Russian Olympic Committee.

"This guy will get banned for life, at least for all Australian events, right? @Australian Open," Dolgopolov, a quarter-finalist in the 2011 Australian Open, said in a message.

The Ukrainian Tennis Federation also took to social media to draw attention to the incident during the match won by Djokovic 6-1, 6-2, 6-4.

"We believe this is the 1st display of the Z symbol of Russia’s war on Ukraine at the international tennis tournament," they wrote on Twitter.

It is not the first time during this year's Australian Open where controversy has arisen over the use of Russian symbols.

A Russian flag was held up by a fan during Ukraine's Kateryna Baindl's win over neutral Russian player Kamilla Rakhimova.

After this incident, Tennis Australia banned displaying the national flags of Belarus and Russia, adding to the existing rule that players from these countries must compete without flags or country recognition.

During the same match at the Rod Laver Arena where the "Z" symbol was seen, Djokovic urged the umpire James Keothavong to give a fan in the crowd a warning for their behaviour who continued to heckle the Serbian former world number one.

"Send him home Rublev, send him home," said the fan.

In response, Djokovic called for the umpire to do something about it.

"Can you tell the front guy to shut up or not?" said Djokovic. 

"Every point, every single point you're not reacting.

"I don't mind if he is supporting him [Rublev]. 

"But for three or four times in a row, he has said things about me."

Meanwhile, American tennis great Billie Jean King has called for organisers of Wimbledon to lift the ban on Russian and Belarusian players at the 2023 tournament, despite all the controversy surrounding their participation at the Australian Open.

"Just keep it the same way as the other ones are - life is too short," said King, whose 12 Grand Slam singles title included the Australian Open in 1968.

The ban in 2022 led to fines for the All-England Lawn Tennis Club and the Lawn Tennis Association.