Brash, loud, and combative, Novak Djokovic's father Srdjan has again stolen the spotlight from his son in the latest off-court controversy to rock the tennis star's career.

This week, Srdjan made headlines again at the Australian Open after the 61-year-old was filmed posing with fans brandishing banned Russian flags, including one featuring Vladimir Putin, in scenes Ukraine's ambassador Thursday slammed as "a disgrace".

Since the invasion of Ukraine, many in Serbia have actively thrown their support behind Moscow, with pro-Russia murals appearing in Belgrade, ultranationalist football hooligans rallying behind the Kremlin's cause, and demonstrators in support of the war taking to the streets.

The controversy in Melbourne came as Djokovic had just booked his place in the semi-finals with a straight-sets thumping of Russian opponent Andrey Rublev at Rod Laver Arena on Wednesday.

But for Srdjan, making waves was nothing new.

Last year, Srdjan took a leading role in defending his son after he was detained and later deported from Australia over his Covid-19 vaccine status.

In the Serbian capital Belgrade, he led boisterous protests filled with flag-waving demonstrators and held his own heated press conferences where he compared Djokovic's plight to that of Jesus Christ.

"They try to crucify Novak too, to humiliate him... He will endure," Srdjan told reporters at the time.

Over the years, Srdjan has stuck to a familiar script, framing the occasional controversy involving Djokovic as an ongoing battle between an ambitious Serb on the international stage and a jealous West.

"The West doesn't like him," Srdjan told Prva TV in 2021.

"They will have to accept that he is the best, and will be the best in tennis history."

Born in a small mining village in impoverished Kosovo, Srdjan moved to Belgrade as a teenager where he pursued a career as a skiing instructor before meeting his wife and starting a family.

Novak was their firstborn and showed early promise in sport, especially tennis.

"We sat with him on a table when he was 10 years old and asked him -- what do you want to be when you grow up? He said he wanted to become the tennis number one, which we completely supported and I dedicated myself to his career," Srdjan told Serbian newspaper Kurir.

But raising a tennis champion proved expensive, especially during the war years in Serbia, when the country was hit with sanctions amid the bloody break-up of Yugoslavia.

Srdjan has said he sold the family's gold for cut-rate prices and even borrowed money from a loan shark to finance his son's early career.

But along with the sacrifices, Srdjan also exhibited a heavy-hand in controlling his son's career -- on and off the court.

"Since he was six, we look after every aspect of his career. What he would work on today, tomorrow, a month or year from now. What he eats. What he drinks," Srdjan said.

"Every aspect and detail of his life is under control."

Srdjan has even admitted to neglecting his other children in the quest to nurture Novak's future and described himself as a "mother, father, coach, physician -- everything".

"Only Novak mattered," he told Serbian media.

"All of us... were irrelevant. Everything was done so he could achieve what he did."