WATCH | Djokovic's father seen posing with pro-Putin protesters at Oz Open

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 after 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.