St. Petersburg: Romanian tennis star Simona Halep withdrew from the St. Petersburg Ladies' Trophy quarter-final against Russia's Natalia Vikhlyantseva due to a knee injury.

Vikhlyantseva, 19, on Friday qualified for the semi-finals, where she will face the winner of the match between Italy's Roberta Vinci and Frenchwoman Kristina Mladenovic, reports Efe.

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Slovakia's Dominika Cibulkova, second seed, also qualified for the semi-finals by beating Russian Elena Vesnina 6-3, 6-3.

World No.4 Halep, 25, has been suffering knee problems since last fall and was eliminated in the first round at the recent Australian Open.