US Open champion Clijsters told officials she is still not fully recovered form a June ankle injury which forced her to also miss Wimbledon and is still concentrating on getting ready for the Open from August 29.
Also out of the field is Wimbledon winner Petra Kvitova, with the world No. 7 suffering with a pulled abdominal muscle. "I am sorry I am unable to play this year but I'm still recovering from an injury that happened at Wimbledon," said the Czech.
But riding to the rescue are the Teutonic trio of Andrea Petkovic, Julia Goerges and Sabine Lisicki. No. 11 Petkovic, captured her second career WTA singles title in Brisbane, and reached quarter-finals at the Australian and French Opens in 2011.
No. 16 Goerges holds the Stuttgart clay title while 26th-ranked Lisicki won on grass at Birmingham and reached the Wimbledon quarters in a revival of the German game which has taken off this season.
The event also includes entries from No. 3 Vera Zvonareva, defending champion Svetlana Kuznetsova and former world No. 1 Ana Ivanovic.