World's No. 1 Novak Djokovic's hopes of participating in the U.S. Open once again suffered another blow as the tournament confirmed that it would respect the United States government's rules to require non-citizens to be fully vaccinated against coronavirus to enter the country.

U.S. Open organizers which does not have its own vaccination rules stated, "Per the Grand Slam Rule Book, all eligible players are automatically entered into the men's and women's singles main draw fields based on ranking 42 days prior to the first Monday of the event. The US Open does not have a vaccination mandate in place for players, but it will respect the US government's position regarding travel into the country for unvaccinated non-US citizens."

The U.S. rule is to ensure visitors or tourists are fully vaccinated against Covid-19 in order to be allowed to enter the country. It appeared that Djokovic, who has made it clear that he will not take the vaccine, will not be permitted an entry. The Wimbledon champion was also known to be banned from playing in the Australian Open due to his anti-vaccination belief.

The 35-year-old three-time champion at Flushing Meadows was included on the entry list for the final Grand Slam of the year on Wednesday. British pair Andy Murray and Emma Raducanu, who is hoping to defend the title she won as a qualifier in 2021, are also on the list.

Serena Williams, a six-time winner of the U.S. Open, was named on the list. She will be  in the field hoping to equal Margaret Court's record of 24 Grand Slam titles at 40 years old. Great Britain's Kyle Edmund is also about to participate in his first singles event at a Grand Slam in two years. The 27-year-old made a dramatic return after suffering from knee injury; he made his comeback at Wimbledon, playing in the mixed doubles.

Former Acting Director of U.S. National Intelligence Richard Grenell has urged President Joe Biden and U.S. authorities to let Djokovic compete at the U.S. Open. He has insisted that he does not want the U.S. Open to go ahead without "one of the best players in the world."

Meanwhile, almost 12,000 people have reportedly signed an online petition calling for the United States Tennis Association (USTA) to work with the country's government to permit Djokovic to compete in the U.S. Open despite his firm refusal to take the Covid-19 vaccine. The main draw at the U.S. Open starts on Aug. 29.

Novak Djokovic Novak Djokovic of Serbia poses with the Wimbledon trophy during the press conference in the Belgrade City Hall on July 11, 2022 in Belgrade, Serbia. Photo by Srdjan Stevanovic/Getty Images