The sports world likely will not be able to return to full normalcy until the development and deployment of a COVID-19 vaccine. That process could take a year to 18 months, as said repeatedly by Anthony Fauci, the nation’s leading infectious disease expert.

But whenever it happens, 17-time grand slam winner Novak Djokovic will face a dilemma, considering his opposition to vaccination that was revealed Sunday in a Facebook chat with other Serbian athletes.

“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. “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,” he said.

Along with that of nearly every other sport, the tennis season is on hold because of the novel coronavirus outbreak, with Wimbledon canceled for the first time since World War II and the French Open moved to September, after the U.S. Open. Whether any of those events are actually played still is up in the air, considering the number of people involved with putting on the tournaments and fans who sit in proximity.

“International circuit = players of all nationalities plus management, spectators and people from the 4 corners of the world who bring these events to life. No vaccine = no tennis,” Amelie Mauresmo, the former women’s No. 1 player and a two-time grand slam winner, wrote March 31 on Twitter.

Djokovic, who previously had not expressed anti-vaccination sentiment, has been described as a devout member of the Serbian Orthodox Church. He said that “before being an athlete, I am an Orthodox Christian” in 2011, the year the church awarded Djokovic the Order of St. Sava, its highest distinction. The Russian Orthodox Church, which exerts political influence over orthodox churches in other European countries, last year came out against proposed Russian laws that would make vaccinations mandatory for public school students, saying in a resolution that parents “should retain the right to make informed decisions regarding the health of their children, including preventive vaccinations, without being subjected to any pressure” and that “persecution of parents for the use of this right is unacceptable.”

Amid a 2018 measles outbreak, the Guardian reported on the growing anti-vaccine sentiment in certain European nations, citing 2017 World Health Organization statistics that showed 640 measles cases per 1 million people in Serbia, which had a vaccination rate of 86 percent. By comparison, the United Kingdom, with a 92-percent vaccination rate, had only 14.4 cases of measles per 1 million people.