WASHINGTON, May 4 (Xinhua) -- Madrid Open organizers said that Serena Williams had withdrawn from the tournament to be held next week because she wasn't ready to compete.

Williams, who won in Madrid in 2012 and 2013, said that 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.