The U.S. Open confirmed Thursday that Serbian star Novak Djokovic cannot play in the tournament next month unless he is fully vaccinated against COVID-19.

The Open doesn't have its own vaccination mandate policy for players but said it will respect the federal government's policy on travel into the country for unvaccinated non-U.S. citizens, according to NBC News. 

The United States requires such travelers to be fully vaccinated to entry the country. The 35-year-old Djokovic, and this year's Wimbledon champion, has declined to be vaccinated, the news outlet also reports.