By Martyn Herman LONDON (Reuters) - 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. 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. Click here to read full news..