World No.1 Novak Djokovic has withdrawn from the Serbian team for the ATP Cup in Sydney, organisers said on Wednesday. The development raises further doubts on Djokovic’s participation in the 2022 Australian Open to be held in Melbourne.

“It was announced Wednesday that World No.1 Novak Djokovic has withdrawn from the ATP Cup. Serbia remains in the competition and will be led by World No. 33 Dusan Lajovic,” said the ATP Cup in its statement.

Reports had emerged in Serbia earlier of Djokovic withdrawing from the tournament but Tennis Australia denied them on Tuesday.

There has been intense speculation over Djokovic’s participation in the event and the Australian Open, which starts on Jan. 17, with the 34-year-old, who is opposed to vaccinations, repeatedly declining to say if he has been inoculated against COVID-19. Djokovic is the men’s singles defending champion at the Grand Slam.

Australian Open organisers have stipulated that all participants must be vaccinated against the coronavirus or have a medical exemption granted by an independent panel of experts.

Djokovic’s withdrawal could mean that the 2022 Australian Open, the first Grand Slam of the season, could be played without any of the Big 3. While Roger Federer has confirmed that he could be out for almost the entire first half of the season with injury, Rafael Nadal is yet to commit to participating in the event after making a recent comeback from a long spell on the sidelines due to injury.