Novak Djokovic's coach Andre Agassi has fired a warning to Roger Federer and Rafael Nadal ahead of the Serb's return in 2018 with the American expecting "something special" from his player.

The 12-time men's singles Grand Slam champion has not played for the last four months with his last action on a tennis court coming during his quarter-finals retirement at Wimbledon. He decided to end his season early in order to focus on recovering from an elbow injury.

Federer and Nadal have dominated the 2017 campaign in Djokovic's absence winning seven and six titles each respectively which includes equally sharing the four Grand Slam between them. The Serbian managed just two titles – Doha Open and Eastbourne – before calling time on his season in July.

Agassi, however, is confident that Djokovic can return to winning ways in 2018 despite struggling for form since winning the French Open in 2016. The American tennis legend went through a similar phase in his career when he dropped out of the top-100 after being the world number one then returned to the summit in under two years.

And Agassi is confident that he can work with Djokovic and get him back to his best in 2018. While the Serb has made it clear that he wants to win more Grand Slams.

"Novak is somebody that is very familiar to me in this intersection of his life between what he's capable of and where he finds himself as he has to approach possibly the most accomplished phase of his life," Agassi said, as quoted by the Metro.

"I've been through that intersection so there's a lot of, not just problem solving – that inspires me, but helping a person that I think is an incredibly generous spirit and is for the game and has multiple wins and so far it's something I'm enjoying trying to contribute.

"Novak is one of those talents that if he feels right on the tennis court it doesn't matter who's on the other side of the net. I was one of those players that it was about being better than one person and keeping it as simple as that and figuring out a way to just get past that," the American explained.

"If you can take the talent of his magnitude, somebody who can shut down the court the way he can, that can play offense the way he can and actually get him to realize there's another human being on the other side of the net and all you have to do is be better than that guy I think you're really going to see something special from him."