Wozniacki was coming off a hard-fought loss to Venus Williams in the final of the ASB Classic in Auckland, New Zealand, on Saturday, and the injury throws into doubt her fitness for the Australian Open.
In other matches, third-seeded Agnieszka Radwanska of Poland beat Alize Cornet of France 6-3, 6-2 and fifth-seeded Angelique Kerber of Germany defeated Lesia Tsurenko of Ukraine 1-6, 6-4, 6-3.
Sixth-seeded Ekaterina Makarova of Russia, seventh-seeded Dominika Cibulkova of Slovakia and Garbine Muguruza of Spain also won while eighth-seeded Flavia Pennetta of Italy lost to Bulgarian qualifier Tsvetana Pironkova 6-3, 7-6 (4).
On the men's side, fifth-seeded Leonardo Mayer beat Benjamin Becker 7-6 (3), 6-2 and sixth-seeded Pablo Cuevas defeated Nicolas Almagro 7-6 (5), 6-4.
At the Hobart International tournament in Tasmania, top-seeded Casey Dellacqua of Australia beat Lauren Davis of the United States 6-4, 1-6, 6-4.
Also, third-seeded Camila Giorgi of Italy overcame 23 double-faults to beat Australian wild-card entry Storm Sanders 5-7, 6-1, 7-6 (6), and second-seeded Zarina Diyas of Kazakhstan defeated Silvia Soler-Espinosa 6-3, 6-4.
Adrian Mannarino of France beat Federico Delbonis 6-1, 6-1 at the Heineken Open in Auckland in the first match of a draw gutted by the late withdrawals of defending champion John Isner, top-seeded David Ferrer and Gael Monfils.