Novak Djokovic's name has appeared in the draw for the first Masters Series event of the year in Indian Wells.
But that is obligatory for any non-US citizen wishing to enter the country.
Djokovic did not take his name off the entry list before Tuesday's draw, and tournament organisers admit they have not yet been able to find out whether he has a viable route into the US.
"Novak Djokovic is on the tournament entry list, and therefore is placed into the draw," the BNP Paribas Open said in a statement.
"We are currently in communication with his team; however, it has not been determined if he will participate in the event by getting CDC (Centers for Disease Control and Prevention) approval to enter the country.