The defending champion Roger Federer has decided to miss next week's Paris Masters and will lose his world number one tennis ranking to Novak Djokovic next week.
Federer says he's very disappointed but he has some injury niggles he doesn't want to take a chance on.
The Swiss great lost to Juan Martin del Potro in the Basel Open indoors final on Monday, meaning Djokovic will return to No. 1 next week, as Federer will not be able to earn enough points to finish the year ahead of Djokovic, says the governing body of men's tennis.
The Association of Tennis Professionals says Djokovic will be officially crowned No. 1 during a presentation at the World Tour Finals in London next week.
Djokovic lost the top spot to Federer in July, but now the Serb will become the first player to finish No.1 in consecutive years since Federer did it four straight times from 2004-07.
Ironically Djokovic may now also pull of the Paris tournament as he says he isn't feeling well.
Spain's Rafael Nadal has also pulled out as he continues to recover from a knee injury.