World number 11 Andrea Petkovic has withdrawn from the Tennis Grand Prix in Stuttgart, which got under way on Monday.

Petkovic competed for Germany in their 3-2 Fed Cup defeat to Russia at the weekend but has withdrawn from this week's WTA Premier event with an apparent thigh problem.

"Really sorry to announce that I have withdrawn from the Porsche Tennis Grand Prix in Stuttgart," she wrote on Twitter.

"It is one of my favourite tournements [sic] and and also one of the few left in my home country.

"Have no words to express my disappointment and sadness but after all it is a decision I had to make in order to avoid any further risk for my health."

The first-round action did get underway on Monday, though, with wildcard Carina Wiffhoft surprising her German compatriot Mona Barthel - ranked 35 spots above Wiffhoft - 7-5 6-3.