Federer replaced Djokovic at the top of the standings after winning Wimbledon in July earlier this year, but has now ceded the position to the Serb after he being forced to pull out of the Paris Masters due to an injury.

The Swiss tennis star said there should be no doubt about Djokovic being the ‘real no 1'.

"We know who the real number one is. It is going to be Novak. I do not think there should be any debate around about that,” News.com.au quoted Federer, as saying.

"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,” he added.

Federer said though he had to let go of his op spot this year, he would make sure that he doesn't have to do such a ‘sacrifice' again.

"I obviously gave it everything I had. I've played so much tennis the last one and a half, two years and I'm happy I got back to world number one,” he said.