Novak Djokovic has lost his aura of invincibility but coach Andre Agassi says nobody should be surprised if the Serb goes on to claim his fourth Wimbledon title this month.

Djokovic has dropped to fourth in singles rankings after an inconsistent season and the 30-year-old's Aegon International triumph on Saturday was only his second title of the year.

"Don't be surprised," eight-time grand slam winner Agassi, who joined Djokovic's team prior to French Open in May, was quoted as saying by the Guardian newspaper.

"Can a guy like this objectively find his way back to the trophy? Heck, yeah he could....That's the plan, that's always the plan – to get better – and the belief in winning has to be yours and yours alone.

"I think there's enough momentum that could build to give that particular dream, hope or objective a real shot."

The American said his growing familiarity with Djokovic has led to a better understanding of the game-plan, which could guide the 12-time grand slam champion back to his best.

"I know him so much better now than I did coming in and that's so important. I can effectively say there is belief in what the plan is and how we're going to go about it," Agassi said.

"It will get more nuanced and layered as we go – it's problem solving and I am enjoying learning, I'm enjoying giving some tools and I have the utmost belief that it's going to make him once again the best of who he is."

Djokovic also has added Mario Ancic, who reached the semi-finals at Wimbledon in 2004, to his coaching team for his SW19 campaign, which starts with a match against Slovakia's Martin Klizan in the first round on Tuesday.