BRUSSELS, Belgium — Top-ranked Justine Henin pulled out of next week's Family Circle Cup because of a knee problem.

Henin said her right knee still feels too sore to compete in the WTA event in Charleston, S.C.

"She does not want to endanger her clay-court season," the Belgian's Web site said.

Henin has won two events so far this season, but lost to Serena Williams 6-2, 6-0 in the quarterfinals of the Sony Ericsson Open in Key Biscayne last week.

She is expected to return at the May 5-11 German Open in Berlin.