Srdjan Djokovic is in Melbourne to support his son as he chases a 10th grand slam title in Australia and a record-equalling 22nd men's singles major overall.
He has been in the player's box for his 35-year-old son's matches, cheering the Serbian into the semi-finals.
The tournament was rocked on Wednesday by a group of pro-Putin agitators staging a rally outside Rod Laver Arena, after Djokovic beat Russian Andrey Rublev to reach the last four.
Rublev has previously expressed his opposition to Russia's war in Ukraine, which has been ongoing since last February.
The Putin supporters chanted and carried flags of Serbia and Russia. One man appeared to be wearing a T-shirt adorned with the letter 'Z' – used as a pro-war symbol in Russia.
Srdjan Djokovic appeared to happily stand with the group outside the stadium court. According to reports, he said: "Long live the Russians."
Tennis Australia banned Russian and Belarusian flags from the event earlier this month, after a spectator was reported to security for displaying one during a match between Ukraine's Kateryna Baindl and Russian Kamilla Rakhimova.
Russian and Belarusian players have not been able to play under their countries' flags since Putin's regime launched its invasion.
In a statement, Tennis Australia reacted to Wednesday's incident, saying: "A small group of people displayed inappropriate flags and symbols and threatened security guards following a match on Wednesday night and were evicted. 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."
Tennis journalist Ben Rothenberg wrote of the Srdjan Djokovic incident: "This is…quite a mess for the #AusOpen, to say the least. The levels of security breakdowns that allowed for this are staggering."
Another tennis reporter, Carole Bouchard, added: "Sorry but they shouldn't warn Srdjan Djokovic after that. They should remove his credential. This is outrageous."
There has been no suggestion from tournament officials that Srdjan Djokovic will face such action, and it remains to be seen whether he attends his son's semi-final against American Tommy Paul on Friday.
Ukrainian WTA player Marta Kostyuk addressed the issue on Twitter with a series of nine exploding head emojis.
Before footage emerged of Srdjan Djokovic alongside the group, Ukraine's ambassador to Australia and New Zealand, Vasyl Myroshnychenko, expressed his dismay.
He wrote on Twitter: "It's a full package. Among the Serbian flags, there is: a Russian flag, Putin, Z-symbol, so-called Donetsk People's Republic flag. It's such a disgrace."