Show me a link where Novak Djokovic is banned from the U.S. Open.
p.s. as another poster added, your state department can give him an exemption to enter. But as it stands now, he cannot enter.
https://www.express.co.uk/sport/tennis/1550879/novak-djokovic-deported-australia-us-open-ban-vn
He might not get to play now in the French Open either, but Boris just relaxed the rules in the UK and if Novak Djokovic follows all the new rules for quarantine, me may be able to play in the Wimbledon.
https://www.marca.com/en/tennis/australian-open/2022/01/16/61e4104c22601d96798b45b9.html