The Serbian will take back the title as the world's number one tennis player from Federer, who clinched the top of the rankings following his victory at Wimbledon in July.
"We know who the real number one is," London24 quotes Federer as saying. "It is going to be Novak. I do not think there should be any debate around about that.
"You do not get to number one by chance. The rankings are something that shows how you have played over a 365-day period. It might all change again in two months at the Australian Open but right now it is clear."