World number two Roger Federer reveals he does not have an age or number of Grand Slam titles in mind for when he might retire and says he is not afraid of "facing off against the best" as he prepares for the ATP World Tour Finals in London.

ATP World Tour Finals
Venue: O2 Arena, London Dates: 21-28 November
Coverage: One match each day live on BBC TV, streamed online & available through iPlayer; text commentary online and on mobiles for every singles match via BBC Sport website; every singles match live on 5live sports extra.