MADRID (AP) — Serena Williams has withdrawn from next week's Madrid Open, saying she wasn't ready to compete.
Tournament organizers say Williams withdrew because she needs more time to train before returning to action.
Williams, a 23-time Grand Slam champion, returned to the tour in Indian Wells this year after a 14-month absence because of the birth of her daughter.
Williams fell to early exits at Indian Wells and the Miami Open in her only previous WTA Tour appearances this year.
Williams, 36, is a two-time champion in the Spanish capital, winning the 2012 and 2013 editions of the tournament.
"We regret the absence of Serena," organiser Manolo Santana said.
"She is one of the great champions of our sport, she has always offered a show to the tournament and we hope to see her again at the Caja Magica in the future."
Poland’s Agnieszka Radwanska has also withdrawn from the Madrid Open, which runs from May 7-13, due to a back injury.
Williams missed the first grand slam of the year at the Australian Open in January and could also be ruled out of the French Open, which is held from May 21 to June 10.