"Personally, I am opposed to vaccination, and I wouldn't want to be forced by someone to take a vaccine in order to be able to travel," Djokovic said in a live Facebook chat. "But if it becomes compulsory, what will happen? I will have to make a decision. I have my own thoughts about the matter, and whether those thoughts will change at some point, I don't know.
"Hypothetically, if the season was to resume in July, August or September, though unlikely, I understand that a vaccine will become a requirement straight after we are out of strict quarantine, and there is no vaccine yet."
A vaccine for COVID-19 is believed to be at least a year away from being made widely available. Several are currently in the testing stage.
Djokovic did not delve into his reasoning for being against vaccination. There is no medical reason why vaccines would be considered unsafe.
Wimbledon already announced its cancellation, and the French Open has been pushed back to a September start due to the pandemic. It's unclear when either the ATP or WTA would resume. Many tournaments require international travel, which has been heavily restricted as more than 2.3 million people have been diagnosed with the virus.
All scheduled tournaments have been postponed or canceled until at least July 13.