A group of protesters gathered outside the U.S. Open entry gates at Flushing Meadows in Queens, New York, on Monday to call for an end to vaccine mandates for travelers after 21-time Grand Slam champion Novak Djokovic, who is unvaccinated against COVID-19, announced last week that he would not be able to participate in the tournament.

Demonstrators greeted U.S. Open goers with signs that read "End the travel mandate now!" and "Novak’s body, Novak’s Choice!" 

US Open fans arrive

Tennis fans move in and out of Arthur Ashe Stadium during the fourth round of the U.S. Open tennis tournament in New York on Sept. 3, 2017. (AP Photo/Frank Franklin II, File)

Members of Families are Essential and Children’s Health Defense and Teachers for Choice were among the demonstrators.

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Djokovic announced on social media that he would not be traveling to New York as a result of travel restrictions that prevent any non-U.S. citizens from entering the country without having received the COVID-19 vaccine.

"Sadly, I will not be able to travel to NY this time for US Open," the Serbian tennis pro wrote on Twitter. "Thank you #NoleFam for your messages of love and support."

Novak Djokovic returns a ball during an exhibition match

Serbian tennis player Novak Djokovic returns the ball during an exhibition match in Visoko, Bosnia and Herzegovina, on July 13, 2022. (Nedim Grabovica/Xinhua via Getty Images)

"Good luck to my fellow players! I’ll keep in good shape and positive spirit and wait for an opportunity to compete again. See you soon tennis world!"

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The United States Tennis Association (USTA) provided a statement last month announcing that while the tournament does not have a vaccine mandate, it will adhere to federal policy.

Rafael Nadal addressed Djokovic’s absence from the U.S. Open at a press conference on Friday, calling it "very sad."

"From my personal perspective, it's very sad news. It's always a shame when the best players of the world are not able to play a tournament because of injuries or because of different reasons," he said.

French Open 2021 Novak Djokovic

Serbia's Novak Djokovic, left, shakes hands with Spain's Rafael Nadal after their semifinal match of the French Open tennis tournament at the Roland Garros stadium in Paris on June 11, 2021. (AP Photo/Michel Euler, File)

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"In this case, not having one of the best players of the history in the draw of a Grand Slam is always an important miss. As I said, it's tough for the fans, tough for the tournament."

He continued. "In my opinion, tough for the players, too, because we want to have the best field possible. But, on the other hand, I repeat what I've said plenty of times — the sport in some ways is bigger than any player."

The Associated Press contributed to this report.