World No. 4 Victoria Azarenka becomes the eighth player in the WTA Top 16 to cite a notable injury, withdraw or retire from a U.S. Open Series tournament this summer. Azarenka pulled out of Cincinnati with a right hand strain.

"It's impossible to play,” she told reporters. "It's important also prior to the U.S. Open. It just doesn't make any sense to make it worse."

Other Top 16 players who have been hurt include No. 3 Kim Clijsters (ankle), No. 6 Petra Kvitova (hip), No. 9 Marion Bartoli (a hand injury affected her play in the Stanford final), No. 12 Agnieszka Radwanska (shoulder), No. 13 Svetlana Kuznetsova (groin), No. 15 Peng Shuai (hip), and No. 16 Dominika Cibulkova (abdominal strain).

Also, the United States’ three top women are all hurt or ill. Serena Williams pulled out of her second round match in Cincinnati with a toe injury, and Venus Williams has not played since Wimbledon due to a hip injury and virus. No. 33 Bethanie Mattek-Sands sustained a shoulder injury at Eastbourne and told TENNIS.com that she is rehabbing eight hours a day to get ready for next week’s tournament in Dallas, but is unsure if she can play it.