The 2004 winner, who has been suffering from a knee injury, was on the list of withdrawals announced by organisers on Monday.
World number 15 Kaia Kanepi (Achilles) also misses out, as does Flavia Pennetta (wrist).
Briton Elena Baltacha, who had already announced she would skip the event to undergo ankle surgery, was also on the absent list.
The quartet are replaced in the main draw by Greta Arn, Johanna Larsson, Garbine Muguruza and Sesil Karatantcheva.
On the men's side, the 2003 runner-up Juan Carlos Ferrero has pulled out, joining Spanish compatriot Rafael Nadal on the sidelines.
Gael Monfils and Juan Ignacio Chela have also withdrawn.