Novak Djokovic has withdrawn from Indian Wells and the Miami Open - the first two Masters Series events of the year - because of US coronavirus rules.
Regulations require any non-US citizen to have a Covid vaccination before entering the country.
Serb Djokovic, 34, told the BBC last month that he had not been vaccinated.
The 20-time Grand Slam winner was included in the draw for both events, but has since posted on Twitter that he knew it was "unlikely" he could travel.
He is likely to make his return to the tour at the Monte Carlo Masters in April.
The Indian Wells draw will be less balanced following the late withdrawal of Djokovic, who was seeded second.
As the next player in line to be seeded outside the tournament's top 32, last year's semi-finalist Grigor Dimitrov will move into Djokovic's space in the draw. A lucky loser from qualifying will fill the Bulgarian's spot in due course.
Djokovic missed the Australian Open in January, being deported from the country after its government cancelled his visa in a row over his vaccine status.
In an interview with the BBC last month, he said that he is prepared to miss other big events in future.
"The principles of decision making on my body are more important than any title or anything else," he said.
"I'm trying to be in tune with my body as much as I possibly can."
By missing the Australian Open, Djokovic was overtaken in the list of overall major titles by eventual winner Rafael Nadal, who secured a record 21st Grand Slam.
Djokovic's first tournament in 2022 came in Dubai in February, where he was beaten by Czech Jiri Vesely in the quarter-finals.
The defeat meant he conceded his world number one ranking to Russian Daniil Medvedev, who claimed his first major title at the US Open in September and is the top seed at Indian Wells.
Russell Fuller, tennis correspondent
Djokovic has very few ranking points to defend before his likely next appearance in Monte Carlo.
In fact, he will be world number one again in a fortnight if Daniil Medvedev fails to reach the quarter-finals here in Indian Wells.
But even though his ranking will not be adversely affected, Djokovic is passing up the opportunity to win two of the biggest titles outside of the Grand Slams.
From a public relations perspective, it would have been so much better to have withdrawn 24 hours earlier.
There are clearly far more important things going on in the world right now, but pulling out after the draw has repercussions for other players as well as the tournament itself.
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