It hasn't exactly been a year to remember for Novak Djokovic who was knocked out of the Australian Open in the round of 64 and has failed to win a title since.

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The former World No.1 and current No.2 has been beaten twice by Australian Nick Kyrgios following his early exit from the Australian Open with the 29-year-old Serbian seemingly on the decline with Andy Murray racing clear atop of the world rankings.

One man who has defied age this year however is Australian Open champion Roger Federer, with Djokovic's former Davis Cup coach Bogdan Obradovic suggesting the Serb should learn from the Swiss star.

"Maybe Djokovic should talk to Federer," he told Belgrade daily Blic.

"They are friends, they have known each other for a long time and the Swiss can certainly give him some good advice.

"Given that Federer was able to return into the top 10 and win this year's Australian Open at the age of 36, I see no reason why Djokovic can't be the World No.1 again."

Djokovic has won 14 matches while losing four so far this year with his Australian Open loss to Denis Istomin sparking a form slump of sorts for the Serbian.

"All other players seem to be galvanized against him while his own motivation appears to be inconsistent and shifting all the time," Obradovic said.

"He is not at his best, his serve keeps fluctuating as do elements in his game which really used to be at the highest level consistently.

"However, it is difficult to play at such a high level indefinitely.

"Murray has a huge advantage in the standings but I am sure Djokovic will be back in contention for the top spot."