Novak Djokovic
Novak Djokovic has already suffered four losses in 2017 Getty

Novak Djokovic should heed the advice of Roger Federer if he wants to regain his world number one ranking, according to his former Davis Cup coach Bogdan Obradovic.

Djokovic started the year well after defeating Andy Murray in the final at Qatar, but the 30-year-old's performances since then have declined sharply.

Djokovic suffered a second round exit at the 2017 Australian Open, losing to wild card Denis Istomin before losing to Nick Kyrgios, both in the Mexican Open and BNP Paribas Open.

The Serb was looking to get his season back on track in the Monte-Carlo Masters but crashed out in the quarter-final to David Goffin, taking his 2017 record to 14-4.

Obradovic believes Djokovic should talk to Federer, who after a five-year drought without a Grand Slam, won the 2017 Australian Open as well as titles in Indian Wells and Miami, rising from 16th to fourth in the world rankings within four months.

"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 number one again," Obradovic said, as quoted on Reuters.

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

With Djokovic recently stating that tennis was not his number one priority anymore, Obradovic has noticed how other players seem ready to take on the reigning French Open champion.

"All other players seem to be galvanised against him while his own motivation appears to be inconsistent and shifting all the time," he added. "He is not at his best, his serve keeps fluctuating as do elements in his game which really used to be at 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."