More than 12,000 people have signed an online petition on change.org calling for the United States Tennis Association (USTA) and the U.S. government to allow to compete in the U.S. Open.

Currently, the 21-time grand slam champion is unable to enter the country due to rules that require travelers to be fully vaccinated against COVID-19.

"There is absolutely no reason at this stage of the pandemic to not allow to play at the U.S. Open 2022. U.S. Government and USTA must work together to allow him to play. If unvaccinated American players can play, as one of the legends of the game must be allowed to play. MAKE IT HAPPEN, USTA!" the petition said.

Immigration issues have somewhat derailed Djokovic's year as his refusal to take the COVID-19 vaccine has hindered his participation in tournaments around the world.

Before the Australian Open kicked off in January, Djokovic was following a period in detention and was unable to defend his title.

He later told the BBC that he would be to maintain his unvaccinated status and he has forgone playing in several tournaments throughout the year including those based in the U.S., such as the Miami Open and Indian Wells.

Djokovic has, however, played in two grand slams this year -- the French Open where he reached the quarterfinals losing to eventual champion Rafael Nadal, and Wimbledon where he defended his title with 4-6 6-3 6-4 7-6 victory over Nick Kyrgios in the final.

Currently unable to enter the United States -- and with his participation in the Australian Open also in doubt due to laws that could ban him from entering the country for a further three years -- Djokovic's next appearance at a grand slam could be the 2023 French Open.

The U.S. Open begins in Flushing Meadows, New York on August 29.

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