LONDON. Roger Federer slid his racket into his bag and walked off into the shadows of London’s o2 Arena on Sunday as his leanest season since 2001 came to a rather predictable end at the hands of Rafa Nadal.The 32-year-old’s 7-5 6-3 defeat in the semi-finals of the ATP World Tour Finals ended his hopes of winning the title for a seventh time and with his ranking now on the slide there is no telling if he will ever return at the season-ender.Federer, who has spent a record 302 weeks as world No.1 during his glittering career, preferred to look at the positives after his 22nd career defeat by Nadal.The Swiss 17-times grand slam champion pointed to his strong finish to a disappointing year, with a final in Basel followed by a semi-final run at the Paris Masters and wins over world No.5 Juan Martin del Potro and Richard Gasquet in London.He also pushed Novak Djokovic hard in Paris where he was a set and a break up and also here this week while on Sunday against Nadal he matched the Spaniard for the first 10 games.The statistics are beginning to stack up against him, however, and inevitable questions are being raised about Federer’s prospects for 2014.His one title this year was on grass at Halle.At Wimbledon, as defending champion, his proud record of reaching at least the quarter-finals at 36 consecutive grand slams ended in the second round, almost unthinkably, against 116th ranked Sergiy Stakhovsky.In between there was a brief experimentation with a larger racket and further humbling losses to the likes of Federico Delbonis in Hamburg and Daniel Brands in Gstad, players he once swatted away in his sleep.The grind of the Tour has also taken its toll on his body with the Swiss suffering a back injury before the U.S. Open.Having split with coach Paul Annacone in October Federer, who slipped outside world’s top-four for the first time since in 10 years in July, was by no means guaranteed his place in the Tour Finals for a 12th consecutive year until his late return to form on indoor courts.Federer’s game scaled the heights at times in London, if only in brief bursts.The majestic forehands and backhands are still there, the backhand slice still fizzes low and the accuracy of his serve still earns him plenty of cheap points. He still makes the game look ridiculously easy at times.Yet, just like golf great Tiger Woods, who still looks unbeatable on his good days, Federer is prone to more regular lapses of concentration, his shot selection can be questionable at key moments and the aura he once had has faded.He also looks a yard slower. "He hasn’t been moving as well this year as he did the year before, and that’s one of the reasons why he hasn’t had much success this year,” Djokovic said this week.Nadal defended Federer to the hilt on Sunday saying he is a "candidate” for the Australian Open next year. And Federer scoffs when asked what it is that makes him want to continue playing the sport.TENNIS DNA"It’s pretty simple; this is what I used to do as a little boy. It’s something that always is there in your DNA,” Federer said. "It’s almost like I started walking at the same time I started playing tennis in some ways.”Yet there is not quite the same conviction when Federer talks about his aims for next year. "Winning titles, winning five titles or something, I guess, something exciting, leaving the tournaments as winner,” he said. "Rankings? if it’s not world No. 1, then I’m not that interested, although it would be nice to stay in the top four, top eight, that kind of thing.”