Clijsters, 37, underwent surgery on her right knee in October and also contracted COVID-19, which disrupted her training and led to the decision.
“I’ve had an intensive few weeks of training with my team. Unfortunately, I am not where I need to be, especially if I want to compete with the best,” Clijsters said on Twitter.
The 34-year-old Sania Mirza and her Belgian partner were awarded wildcard entries for both events. Sania’s father and coach Imran Mirza too confirmed her exit.
The WTA 1000 Miami Open runs from March 23 to April 3 while the Charteston WTA 500 event is from April 5 to 11.
Last January, Sania returned to the WTA tour following a two-year layoff due to an injury and then her pregnancy.
She made a smashing comeback to claim the doubles title at the Hobart International and then led India to their maiden playoffs in the Fed Cup, now called the Billie Jean King Cup.
Sania’s return, however, was disrupted by the pandemic which forced all sporting events to either be cancelled or postponed.
The former world No. 1 doubles player considered getting back to action at the Australian Open in February but a bout with the coronavirus delayed Sania’s plans.
Sania Mirza returned to the court with the Qatar Open earlier this month, where she and her Slovenian partner Andreja Klepac lost in the semi-final of the WTA 500 tournament.
The Indo-Slovenian pair bowed out in the second round of the Dubai Open last week.