Williams, who missed the hardcourt season with what had been described as a viral illness, withdrew from the United States Open minutes before she was due on court at Arthur Ashe Stadium for her second-round match against No. 22 Sabine Lisicki.
Williams, 31, was unseeded for the first time since 1997, when she advanced to the final in her Open debut. Appearing in her 13th Open, she had pulled the curtain back on a game that looked robust, if a tad rusty, in her 6-4, 6-3 victory over Vesna Dolonts on Monday. She had aspired to become the first Open women’s singles champion over 30 since Martina Navratilova in 1987.