World No 11 Petra Kvitova has been forced to withdraw from the St Petersburg Open quarter-finals due to illness.

The No 3 seed was set to face Russian Ekaterina Alexandrova today. 

The 29 year-old said: "I'm really sorry to withdraw from the St Petersburg Ladies' Trophy due to illness.

"I wasn't feeling well during my match yesterday and hoped I would feel better today, but unfortunately, that's not the case. I'm sorry not to play in front of the fans here in this beautiful city. I wish the tournament a great finish and hope to be back again next year."

The Shenzhen Open champion, Alexandrova, advances into the semi-final where she will face No 2 seed Kiki Bertens or qualifier Anastasia Potapova.