Tennis ace Martina Hingis is under investigation after testing positive for cocaine. The 27-year-old Swiss player announced her retirement from the sport on Thursday after admitting she failed a drug test at the Wimbledon tennis championships in England earlier this year.

Hingis, who has endured a string of ankle injury problems in recent years, insists she has never used cocaine.

She says, "I have tested positive but I have never taken drugs and I feel 100 per cent innocent. The reason I have come out with this is because I do not want to have a fight with anti-doping authorities. Because of my age and my health problems, I have also decided to retire from professional tennis."

Hingis won five Grand Slam titles during her career. She retired from tennis in 2003 due to her ankle, but re-emerged in 2006 before being forced to prematurely end her season again last month due to hip problems.

-Martina Hingis Pictures

(This news article provided by World Entertainment News Network)