World number one Novak Djokovic has withdrawn from this week's Indian Wells Masters event with the Serb unable to enter the United States.
The US requires international visitors to be vaccinated and proof will be required until at least 10 April.
Djokovic missed last year's US Open because of his vaccination status.
"World number one Novak Djokovic has withdrawn from the 2023 BNP Paribas Open. With his withdrawal, Nikoloz Basilashvili moves into the field," organisers said in a statement.
Indian Wells - one of the most prestigious tournaments on the tennis calendar outside of the Grand Slams - starts on 6 March.