Novak Djokovic on Wednesday confirmed his withdrawal from this month's ATP Masters tournaments in Indian Wells and Miami due to US government Covid-19 travel regulations.
Djokovic, who is not vaccinated, said on Twitter that rules requiring non-US citizens to be vaccinated before entering the United States had forced his withdrawal.
"I knew it would be unlikely I'd be able to travel," Serbian star Djokovic wrote.
"The CDC (Centers for Disease Control) has confirmed that regulations won't be changing so I won't be able to play in the US. Good luck to those playing in these great tournaments."
Djokovic's participation at the two prestigious US tournaments had been shrouded in uncertainty for weeks given the US travel restrictions.
However the 34-year-old 20-time Grand Slam singles champion had been named in the men's draw for Indian Wells on Tuesday despite doubts over his status.
"Novak Djokovic is on the tournament entry list, and therefore is placed into the draw today," tournament chiefs said on Tuesday.
"We are currently in communication with his team; however, it has not been determined if he will participate in the event by getting CDC approval to enter the country."
Djokovic is a five-time champion at Indian Wells, where organisers have said proof of full vaccination will be required for spectator entry to the tournament venue in the California desert.
Djokovic was barred from the Australian Open in January after officials said he did not meet requirements for unvaccinated travellers trying to enter the nation.
His visa was eventually canceled and, after a legal appeal failed, he departed without playing.
Indian Wells organisers said Wednesday that Djokovic's place in the main draw had been taken by Grigor Dimitrov, with a "lucky loser" from qualifying taking the Bulgarian's berth.