A billboard depicting Serbian tennis player Novak Djokovic on a building in Belgrade, Serbia, Thursday, Jan. 6, 2022. The Australian government has denied No. 1-ranked Novak Djokovic entry to defend his title in the year's first tennis major and canceled his visa because he failed to meet the requirements for an exemption to the country's COVID-19 vaccination rules. (AP Photo/Darko Vojinovic)