NUREMBERG, Germany (AP) — Home favorite Laura Siegemund was forced to withdraw during her second-round match at the Nuremberg Cup on Wednesday, while top-seeded Kiki Bertens and Yulia Putintseva both advanced.

The fourth-seeded Siegemund suffered a right knee injury with the score 5-5 in the second set against Barbora Krejcikova of the Czech Republic. Siegemund, who was assisted with a stretcher off the court, had won the opening set 6-4.

Germany's Fed Cup captain Barbara Rittner said Siegemund had likely suffered ligament damage and that "she won't be able to play in Paris" for the French Open.

Defending champion Bertens advanced to the quarterfinals by defeating Annika Beck of Germany 7-5, 6-2, and Putintseva, the No. 2, followed suit with a 6-4, 6-0 win over Yanina Wickmayer of Belgium.

Bertens next plays fifth-seeded Alison Riske of the United States, while Putintseva will face Sorana Cirstea of Romania.

Also Wednesday, Japan's Misaki Doi defeated Oceane Dodin of France 3-6, 6-0, 6-3 to line up a quarterfinal against seventh-seeded Yaroslava Shvedova, who defeated Tatjana Maria of Germany, 6-2, 6-4.

Carina Witthoeft was the last German remaining in the tournament after a 6-1, 7-5 win over compatriot Julia Goerges. Witthoeft next plays Krejcikova.