"Unfortunately my body has not recovered the way I'd hoped after the Australian Open and I have not been able to adequately prepare for Indian Wells and Miami," Barty said in a statement released by organizers of Indian Wells, which starts on Wednesday in the California desert.
"I don't believe I am at the level necessary to win these events and as a result I have decided to withdraw from both tournaments," added Barty, who would have been seeking a third straight title in Miami later in March.
Barty said she hoped to be back on court representing Australia in the Billie Jean King Cup in April.
"After missing the BJK Cup last year I can't wait to wear the green and gold again," she said.
In January, Barty became the first Australian to win her home Grand Slam in 44 years.
She was 5-1 down in the second set against American Danielle Collins but came storming back to triumph 6-3, 7-6 (7/2).
Barty captured her third Grand Slam title after her breakthrough French Open success in 2019 and Wimbledon last year.
She joined Serena Williams as the only active players to win majors on all three surfaces.
Collins also pulled out of Indian Wells due to a nagging injury. Her status for Miami remains uncertain.