World number two women's tennis player Kim Clijsters has been injured at the Sydney international tournament, less than one week before the start of the Australian Open.

The injury occurred with Clijsters's first serve during a warmup for her match against Italian Francesca Schiavone. The Belgian player plans to undergo tests to see if she can play next week.

In other matches, another Belgian, fifth-seeded Justine Henin-Hardenne, reached the semifinals when Nadia Petrova of Russia withdrew before their quarterfinal match.

Henin-Hardenne takes on sixth-seeded Svetlana Kuznetsova of Russia, who overpowered Ana Ivanovic of Serbia and Montenegro 7-6, 6-3.

In men's action, top seed Lleyton Hewitt of Australia advanced to the quarterfinals with a 6-1, 6-4 win over Austria's Jurgen Melzer.

Eighth-seeded American James Blake had a walkover against Spain's Carlos Moya. Igor Andreev of Russia held off Australia's Peter Luczak 6-7, 7-6, 7-6.

Frenchman Arnaud Clement and Dmitry Tursonov of Russia also advanced.

The hard court tournament is one of the final warm-ups for the first major tournament of the year, the Australian Open, which starts Monday in Melbourne.

Some information for this report was provided by AFP, AP and Reuters.