Australian Open organisers have issued a reminder to players and their entourages about their policy on "inappropriate flags" after a video emerged showing Novak Djokovic's father posing for pictures with fans holding Russian flags.
Four fans with "inappropriate flags and symbols" were questioned by Victoria Police following Wednesday's quarter-final between Djokovic and Russia's Andrey Rublev.
A video also posted on social media showed one supporter on the steps of Rod Laver Arena holding up a Russian flag with the image of President Vladimir Putin on it.
Late on Wednesday another video showed Djokovic's father Srdjan posing for pictures with fans holding Russian flags.
"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," Tennis Australia said in a statement on Thursday.
"We continue to work closely with event security and law enforcement agencies."
Russian and Belarusian flags are banned from Melbourne Park during the tournament after a complaint from the Ukraine ambassador to the country.
Belarus is a key staging ground for Russia's war in Ukraine, which Moscow terms a "special operation".
Photos on social media also showed one fan in the crowd during Wednesday's match with a "Z" on his shirt.
Russian forces have used the letter "Z" as an identifying symbol on their vehicles in Ukraine following the invasion. Some supporters of the invasion have also used the sign.
Russian and Belarusian players were banned from Wimbledon last year but are able to compete as individual athletes without national affiliation at Melbourne Park.
Their flags are not displayed beside their names in TV broadcasts, as is the case for other players, and their nation is not indicated on draw sheets.
