The tennis career of twice Wimbledon champion Petra Kvitova was under threat after she suffered severe injuries to her playing hand defending herself from a knife-wielding intruder in her apartment Tuesday. The Czech world No. 11 said before undergoing surgery that the attack had left her "shaken, but fortunate to be alive". "In my attempt to defend myself, I was badly injured on my left hand," Kvitova said on Twitter. "The injury is severe and I will need to see specialists, but if you know anything about me I am strong and I will fight this." Her publicist Katie Spellman told Reuters in an email that Kvitova was undergoing "four hours of hand surgery", adding that more details would be available later. Kvitova was attacked in her flat in the city of Prostejov, about 260 kilometers (160 miles) southeast of Prague, the location of a tennis club where she, men's world No. 10 Tomas Berdych and other top-ranked Czech players often train. The 26-year-old had been due later in the day to play a charity event in the Czech Republic's second biggest city Brno alongside compatriot Lucie Safarova. The pair have been fixtures in the Czech Fed Cup team that has won the premier women's team tennis event in five of the last six years. "What happened to Petra, can happen to any of us. I got goosebumps from it," Safarova told online news website Aktualne.cz. Czech-born tennis great Martina Navratilova said on Twitter: "Just finding out about @Petra_Kvitova and the awful stabbing and injury to her hand - pulling for you Petra." World No. 3 Agnieszka Radwanska also voiced support for Kvitova. "My thoughts are with @Petra_Kvitova. Terrible news," she Tweeted. Karel Tejkal, spokesman for the Czech Fed Cup team, told Czech media the morning attack had been "a random criminal act" and that Kvitova had not been specifically targeted. Media reported the intruder presented himself to Kvitova as a boiler inspector. "What has happened to me was not pleasant at all, but it is already behind me," Kvitova said in an earlier statement issued on the Fed Cup team's Facebook page. "The main thing for me now is that the doctors will determine how my hand is doing. I trust them and I believe that it will end well." The hard-hitting left-hander has been in the world's top 10 for most of the past five years, rising to No. 2 in 2011 when she won the first of her two Wimbledon singles titles. She slipped in the rankings this year but showed improved form in recent months, winning the Wuhan Open title in October and the season-ending WTA Elite trophy in November.