Wimbledon champion Barbora Krejcikova has withdrawn from next month's tournaments at Indian Wells and Miami because of a back injury that has kept her out of action since November.
The world No. 16, a surprise champion at the All England Club last year, sustained the injury during the Tour's Asian swing of tournaments and appeared hampered by it at the WTA Finals in Riyadh, where she reached the semifinals.
The 29-year-old Czech skipped the Australian Open in January, saying she needed more time for her injury to heal.
Austria's Julia Grabher will take Krejcikova's place in the main draw at the BNP Paribas Open, which begins March 5.
The Miami Open kicks off March 18.
Reuters contributed to this report.