The Belgian downed China's Meng Yuan 6-4, 6-2 to book her third round berth but needed medical treatment on her lower back and said she was not confident of making her next match, scheduled for Saturday.

Asked if she could continue, she replied: "I'm sort of waiting every day to see how it feels, so I can't tell you now."

Clijsters said the back problem, a complication arising from a right hip injury sustained in a Sydney warm-up tournament, was particularly annoying because otherwise she was playing excellent tennis.