Former Wimbledon finalist Sabine Lisicki revealed Wednesday she has undergone surgery for a torn knee ligament which she suffered at the start of the week on the WTA tour. The 31-year-old German hurt her left knee in a first-round doubles match in Linz on Monday alongside British playing partner Jodie Burrage and was forced to retire at 6-5 up in the opening set. Lisicki said an MRI scan revealed a torn anterior cruciate ligament and that she had undergone surgery. "It's going to be a very tough & long road back but I'm luckily surrounded by the best medical team!" she wrote on Twitter, alongside a picture of herself on crutches with her knee heavily strapped. Lisicki lost the 2013 Wimbledon final to France's Marion Bartoli, but has struggled in recent years. After just over a year out of tennis to recover from glandular fever, she picked up her first win on tour this season in August. Having been ranked a career-high 12th in 2012, successive ankle and shoulder injuries have set her back. She is currently 690th in the world. ryj/mw