Ukrainian tennis player Marta Kostyuk said Friday it was "very upsetting" to see Novak Djokovic's father posing alongside a Russian flag with President Vladimir Putin's face on it at the Australian Open.

The 20-year-old Kostyuk was speaking after defeat in the women's doubles semi-finals at Melbourne Park, where there is a ban on Russian and Belarusian flags.

A group of Russian fans flouted the ban on Wednesday night and also chanted pro-Russian and pro-Putin slogans.

Djokovic's father Srdjan was filmed posing with a man holding a Russian flag with Putin's face on it. The man was wearing a T-shirt with a Russian pro-war "Z" on it.

Asked by reporters if she thought Djokovic's father should be banned from Melbourne Park, where the Serbian player is in the semi-finals, Kostyuk said: "That's a lot of responsibility on me.

"I don't know what the rules are, I don't know what the tournament is allowed to do... but this kind of thing can't be left unseen.

"It doesn't matter who you are, nobody is allowed to do it.

"It's very upsetting."

But Kostyuk was hesitant to say much more, fearing a backlash from Djokovic fans.

"No matter what I say I will be hated until the rest of my life, especially by very aggressive Novak fans," she said.

"People know that a lot of -- not everyone -- but Novak has very aggressive fans because I know this and I have experienced this in the past."

Kostyuk, whose country was invaded by Russia last year, said she was surprised and hurt to see Russian flags in the stands and around the tournament despite the ban on them.

"It hurts a lot because there were specific rules, they were printed out outside that this is not allowed to bring flags and so on," said Kostyuk.

"Really hurts that they were out there for some time, they were on the court, in the stands as well.

"I don't know, I just don't understand, it really hurts and I don't understand how this can be possible."