Novak Djokovic's (35) father Srdjan said earlier on Friday he would not attend his son's semi-final against Tommy Paul (25) after a video emerged showing him posing at Melbourne Park with fans holding Russian flags.
Earlier this week, police questioned four fans after Djokovic's quarter-final win over Andrey Rublev (25) after a video on social media showed a fan holding up a Russian flag with the image of President Vladimir Putin on it.
Russian and Belarusian flags are banned from Melbourne Park during the Australian Open after a complaint from the Ukraine ambassador to the country last week. Belarus is a key staging ground for Russia's war in Ukraine, which Moscow terms a "special operation".
"It hurts a lot because there were specific rules, they were printed out outside that this is not allowed to bring flags," Kostyuk told reporters after bowing out of the women's doubles competition with Elena-Gabriela Ruse (25).
"It's not impossible, but you're not allowed to bring out the flags and so on. It really hurts that they were there for quite some time.
"They were there on the court, in the stands as well and I just don't understand as well. It really hurts and I don't understand how this can be possible."
Djokovic will continue his bid for a record-extending 10th Australian Open title and 22nd Grand Slam crown to match Rafael Nadal (36) when he takes on unseeded American Paul later on Friday.
