Charleston - Past champion and No 6 seed Jelena Jankovic withdrew from the Family Circle Cup with a right foot injury about two hours before she was scheduled to play for a spot in the quarter-finals.
Jankovic, the 2007 winner and a finalist two years ago, was scheduled to face Danka Kovinic from Montenegro in the last of the round of 16 matches on Thursday night.
Instead, Kovinic advanced to face defending champion Andrea Petkovic, who improved to 10-0 at the Family Circle with a 6-4, 6-4 victory over American Madison Brengle.
Jankovic won her opening match on Tuesday night over Tatjana Maria in three sets.
Jankovic is the second top seed to withdraw this week. No 2 seed Ekaterina Makarova pulled out on Wednesday because of a stomach illness.