With Novak Djokovic back in his native Serbia, unable to compete in the Australian Open because he is not vaccinated against the coronavirus, a big question mark looms over what comes next for the world’s top male tennis player.

The French authorities said this week that players must be vaccinated to compete in the French Open — the next of the four Grand Slam tournaments, scheduled for May.

If Mr. Djokovic refuses to get vaccinated, he is likely to miss a second major tournament in a row, reflecting a major shift in how public officials approach Covid requirements and potential exemptions. As emblematic as Australia’s refusal to give Mr. Djokovic special treatment has been, it might just be the beginning.

The authorities in Spain, where Mr. Djokovic owns a house, have urged him to “lead by example” and get vaccinated. In Monte Carlo, where Mr. Djokovic also has a house, the organizers of a tournament that he has previously won said they were awaiting guidelines from the French government for the 2022 edition in April.

Mr. Djokovic might be able to compete in Wimbledon in June, but under current guidelines he could be barred from competing in the U.S. Open a few months later, since foreign travelers must be vaccinated to enter the United States, with very limited exceptions.

After France adopted a Covid pass law on Sunday requiring people to be vaccinated to enter restaurants, cinemas and sporting arenas, the country’s Sports Ministry said that no exemption would be made for athletes.

“Who would understand if we asked our citizens to make an effort and respect the rules if we authorize some to get out of them?” Stanislas Guerini, the leader of President Emmanuel Macron’s party, said on French radio this week. He called Mr. Djokovic’s behavior in remaining unvaccinated “irresponsible.”

The French Open is scheduled to begin on May 22, and Mr. Djokovic is chasing a record 21st Grand Slam title. He, Roger Federer and Rafael Nadal have each won 20.

Mr. Djokovic is one of only three top-100 men’s players to be unvaccinated, and some of his rivals welcomed the French decision.

“At least they’re saying, ‘OK, no unvaccinated players are allowed to play in the French Open,’” said Alexander Zverev, who is currently world No. 3 in men’s tennis. “We know that now in advance, and I can imagine there’s not going to be any exemptions, and that’s OK.”