SYDNEY, (Reuters) – Novak Djokovic pulled out of the Serbian team at the ATP Cup in Sydney. Event organizers announced this on Wednesday. This raises doubts about whether or not the number one world player will be defending his Australian Open title next month.

Djokovic has come under intense scrutiny for his participation at both events. The 34-year old, who opposes COVID-19 vaccines, has repeatedly declined to confirm if he was inoculated.

Australian Open organizers stipulate that every participant must have been immunized against the coronavirus and have received a medical exemption by an independent panel.

Australian Open organisers Tennis Australia, and the global men’s tennis governing organization ATP didn’t immediately reply to inquiries for comment.

ATP Cup organizers stated that Serbia’s team would be led now by Dusan Ljubic, the world number 33.

Djokovic’s current ranking in the world, Serbia was given top billing. They were placed in Group A with Norway, Chile, Spain, and Spain during the draw.

Djokovic is currently tied for 20 major titles in Australia with Roger Federer, Rafa Nadal, and has already won nine Australian Open titles.

Last month, his father Srdjan said to a Serbian TV channel that Djokovic was likely to withdraw from the major. He claimed Tennis Australia’s position on mandatory vaccination was equivalent of “blackmail”.

The season-opening ATP Cup saw Austria fail to meet the eligibility criteria after Dennis Novak and Dominic Thiem resigned. France was replaced.

Russia will miss Aslan Karatsev, Asrey Rublev, and the 2021 winner Russia.