Rafael Nadal will finish the year as world number one after Roger Federer was ruled out of the Paris Masters.

Federer had been chasing down Nadal and moved a step closer with victory at the Swiss Indoors in his hometown of Basle, but a back injury has put paid to his hopes of overhauling the Spaniard in the ATP standings.

Despite reducing Nadal's lead at the top to 1,460 points, it now appears the Swiss star's focus will be on the ATP Finals in London.

Federer had already conceded that such a comeback in the standings was unlikely, however, insisting his focus was on victory in Switzerland, which he assured with a win over Juan Martin del Potro in the final on Sunday.

"It is not a priority because it is too far away," he told Tagesanzeiger earlier in the tournament.

"I understand that people ask me about it. But it would be a mistake if I were to think about it all the time. I do not play for that.

"I want to win here, because it's Basel, and in London, because it's the World Tour Finals."