Novak Djokovic had previously said that playing in the U.S. Open would be unlikely without a relaxing of travel rules for foreign visitors to the United States.Credit...John Minchillo/Associated Press

Since then, countries like France and Britain have relaxed their travel restrictions, which allowed Djokovic, who has had Covid-19 at least twice but has steadfastly refused to get vaccinated, to compete. Yet on Thursday, Djokovic was forced to withdraw from the U.S. Open. Still not vaccinated, he was not allowed to come to New York.

The United States has lifted many of its restrictions related to the coronavirus and travel, but unvaccinated foreigners are still not allowed to enter the country, leaving one of the top stars in men’s tennis unable to play in one of the most important tournaments of the year.

“Sadly, I will not be able to travel to NY this time for US Open,” Djokovic wrote on Twitter on Thursday morning, hours before the tournament’s organizers selected matchups for the tournament, which is scheduled to start Monday. He added: “I’ll keep in good shape and positive spirit and wait for an opportunity to compete again.”

In a statement about Djokovic’s decision to pull out of the U.S. Open on the morning of the draw, Stacey Allaster, the tournament director, said it was “very unfortunate that he would be unable to compete at the 2022 U.S. Open.”

Djokovic is the only one in the top echelon of men’s singles players to remain unvaccinated. That decision, criticized by other greats of the game including Rafael Nadal, has sparked a clash pitting his stalwart beliefs in personal freedom and skepticism of established science against the politics and policies of international public health.

It has also turned Djokovic, not for the first time, into a lightning rod in the broader debate about Covid-19 restrictions. Long before scientists said it was safe to gather in large groups in 2020, he held a tennis exhibition that became something of a superspreader event in Serbia, his home country.

He has argued that vaccination should be a personal decision rather than a requirement to play, and earlier this year said he was willing to skip Grand Slam tournaments and forgo championships to remain unvaccinated. At the Australian Open, with Djokovic absent, Nadal edged ahead in their generational battle for the most Grand Slam titles in men’s singles.

Djokovic’s refusal to be vaccinated set off a political firestorm in January. As he was boarding a plane for Australia, he announced he had qualified for an exemption to enter the country to play in the Australian Open, the first Grand Slam tournament of the year, because he had recently recovered from Covid-19.

At the time, Djokovic was following the rules that tournament organizers had provided, rules that had supposedly been approved by state and federal governmental authorities. However, by the time his plane landed, the controversy had exploded on social media and reached the highest levels of the Australian government.

Immigration officials detained him at the airport and sequestered him in a hotel for immigrants seeking political asylum. After a twist-filled ordeal, Djokovic ultimately left the country without defending his singles title from 2021. It ended with a ruling by a three-judge panel that affirmed the Australian government’s decision to cancel Djokovic’s visa, siding with the administration of Scott Morrison, the prime minister at the time, which said Djokovic’s celebrity threatened the country’s efforts to vaccinate its citizenry.

Because under Australian law any person whose visa has been canceled cannot return for three years, Djokovic will need a special exemption to get into the country for next year’s Open.

After the debacle in Australia, Djokovic spent several weeks away from the game, then resumed playing where he could.

“I was not feeling great generally,” he said of that time earlier this summer. “Mentally, emotionally, I was not at a good place. I wanted to play, but at the same time when I went out on the court in Dubai, was the first tournament of the year, I just felt so much pressure and emotions happening. I wasn’t feeling myself on the court. I realized at that point that it’s going to take some time, that I have to be patient, and sooner or later I will get myself in the state, optimal state, where I would like to be.”

While many countries do not require foreigners to be vaccinated, many still do, including the United States and Canada. Health officials have said in part that people who are not vaccinated risk hospitalization and death at much higher rates than people who have been vaccinated.

After winning his 21st Grand Slam singles title at Wimbledon in July, Djokovic said it was unlikely that he would play in the U.S. Open.

“I’m not vaccinated and I’m not planning to get vaccinated so the only good news I can have is them removing the mandated green vaccine card or whatever you call it to enter United States or exemption,” he said, adding, “I don’t think exemption is realistically possible. If that is possibility, I don’t know what exemption would be about.”

The United States Tennis Association said earlier this summer that it would not seek an exemption on Djokovic’s behalf. “The U.S. Open does not have a vaccination mandate in place for players, but it will respect the U.S. government’s position regarding travel into the country for unvaccinated non-U.S. citizens,” the U.S.T.A. said in a statement announcing the tournament entry list in July.

Tournament officials and Djokovic’s team, however, remained in contact throughout the summer.

Djokovic has won the U.S. Open men’s singles title three times, most recently in 2018, but has long had a prickly relationship with the event. He has often been booed and heckled by fans who see him as a tennis villain and an interloper in the rivalry between Nadal and Roger Federer.

In 2020, Djokovic was defaulted from the tournament after he swatted a ball in frustration, inadvertently hitting a line judge in the throat, in the first set of his fourth-round match. He quickly apologized and accepted the ruling.

Last year though, Djokovic finally achieved something that had remained elusive as he piled up championships.

He entered the U.S. Open with the chance to sweep all four Grand Slam titles in a single year, something no man had accomplished since 1969. (Players were allowed at the tournament last year simply by testing negative.)

Djokovic made it all the way to the final, where Daniil Medvedev of Russia beat him in straight sets. But in the final games, the crowd rallied behind Djokovic, the cheers growing louder and louder, bringing him to tears on a final changeover, when he sobbed into a towel.

“My heart is filled with joy, and I am the happiest man alive because you guys made me feel that way on the court,” he said during the post-match award ceremony. “I never felt like this.”

The warm memories were not enough to persuade Djokovic to get vaccinated, but they may have played a role in his timely withdrawal from the tournament. By pulling out before the draw, Djokovic helped organizers reset the seedings for the tournament without throwing it out of balance.

Djokovic, 35, is giving up a chance to draw even with Nadal for the most men’s singles Grand Slam titles. Nadal has 22 and Djokovic has 21.

While Djokovic has plenty of critics inside and outside the game for his refusal to get vaccinated, he does have support among some players, both current and former. John Isner of the U.S. has called his inability to compete ridiculous. Medvedev said Thursday that he wished Djokovic was able to play.

John McEnroe, the ESPN commentator and four-time U.S. Open singles champion, said Wednesday that “it’s a joke if he’s not allowed to participate here.”

“It’s been very unfortunate for him and for tennis,” said McEnroe, who is vaccinated and boosted. “It’s just a shame this whole year.”