The former world No.1 Martina Hingis has expressed doubts over making a surprise return at the London Olympics after countryman Roger Federer invited her to play mixed doubles for Switzerland.
The 30-year-old, five-time grand slam winner, played in the pro-am on opening day at the San Diego Open, then all but ruled out a return.
Hingis dominated tennis from 1997-1999 but quit the game in 2007 without contesting a positive test for cocaine after proclaiming her innocence.
Were she to reconsider the offer to play in the Olympics, Hingis would then have to make a return to the WTA, if only in doubles, make herself available for the Swiss Fed Cup team and also become available for doping tests.
