Serena Williams will lose her place as world number one to Angelique Kerber after the BNP Paribas Open following her withdrawal from the event in Indian Wells with a left knee injury.
Williams has not featured on the WTA Tour since claiming an Open Era record 23rd grand slam title at the Australian Open in January as she cuts down the number of tournaments she plays in.
The 35-year-old was expected to feature at Indian Wells and the Miami Open this month but, after missing a number of practice sessions, she has been forced to pull out of both events.
That decision means Kerber will return to the top of the rankings no matter how she fares in the tournament.
Williams' place in the Indian Wells draw has been taken by Karolina Pliskova after a reshuffle, the third seed awaiting the winner of Monica Puig and Danielle Collins in the second round.
"Sadly, I have to withdraw from the BNP Paribas Open in Indian Wells and the Miami Open," Williams said in a statement.
"I have not been able to train due to my knees and am disappointed I cannot be there. I will keep moving forward and continue to be positive. I look forward to being back as soon as I can."
Williams only returned to Indian Wells in 2015 after a 14-year boycott following an ugly incident that saw the American booed while playing there in 2001.
She reached the semi-finals in her first year back - losing to Simona Halep - before reaching the final 12 months ago, only to be beaten by Victoria Azarenka.