As of now, Novak Djokovic can't play at the US Open but there are alleys for him to end up in New York if certain things happen.
It's highly unlikely that those things would happen as essentially the best bet for him to be in New York is a special exemption from the US president himself. Considering how strict the Biden administration has been on the whole COVID pandemic, it's unlikely that it will come but fans are still hoping. They are creating petitions, calling on politicians with a group of fans even writing to the president himself.
None of that is lost on Djokovic who is currently vacationing with family somewhere in the Mediterranean. The Serbian took the social media to write fans a letter thanking them for having his back during this time:
"I just wanted to take a moment and say to all of you how grateful I am to see so many messages of support and love from all around the world these days. I wasn’t expecting it, and that’s why it feels so mindblowing. Just wanted to say THANK YOU. It feels special that people connect with my tennis career in such a loving and supportive way and wish for me to continue to compete. I am preparing as if I will be allowed to compete, while I await to hear if there is any room for me to travel to US. Fingers crossed!"
As you can see above, Djokovic is holding out hope that he will be able to travel to the US which some fans think is an indication that his team has a way for him to be there. Time will tell.