Roger Federer admits he 'fell into a negative spiral'
But 17-time grand slam winner vows to keep playing and fight for spot in World Tour Finals

Roger Federer admitted he made serious errors in his planning which have contributed to a disastrous 2013 campaign but insisted retirement was not on his agenda.
The 17-time grand slam title winner has slumped to number seven in the world and eight in the race for the World Tour Finals, and failed to make a final at any of the four majors, a run of disappointments that has led many in the sport to predict the end of the road for the 32-year-old.
The Swiss, who split last week with coach Paul Annacone after more than three years, confessed he could have done things differently.
“I played matches that I should never have played,” said Federer, ahead of his participation in his home Swiss Indoors event starting on Monday.
“I should have left in Indian Wells [last March, with back pain] before the quarter-finals against [Rafael Nadal]. This summer, I should not have tried to play on clay in Hamburg and in Gstaad.
“But things always look better in hindsight. I wasn’t able to train as I wanted during my seven-week break following Indian Wells, I fell into a negative spiral.”