Novak Djokovic pulled out of this weeks ATP Cup in Sydney, heightening doubts about his participation in the upcoming Australian Open. "World No. 1 Novak Djokovic has withdrawn from the 2022 ATP Cup," event organizers announced Wednesday. "Team Serbia will now be led by world No. 33 Dusan Lajovic." Djokovic, 34, has declined to confirm his COVID-19 vaccination status, prompting speculation about whether he is planning to travel to Melbourne to defend his Australian Open title. Djokovic and members of his traveling party must be inoculated to enter Australia. The nine-time Australian Open champion currently shares the mens singles record with 20 Grand Slam titles, tied with rivals Roger Federer of Switzerland and Rafael Nadal of Spain. Action gets underway in Melbourne on Jan. 17.