Andre Agassi believes Novak Djokovic is capable of overcoming Rafael Nadal should they meet in the semi-finals at Roland Garros, despite the Spaniard's "incredible" performances so far at this year's French Open.

Following a two-year struggle for form and fitness, Nadal appears back to his ominous best on clay in 2017 and is yet to drop a set in reaching the quarter-finals in Paris, where he is aiming to add to his record haul of nine singles titles.

By contrast, reigning champion Djokovic has endured an uncharacteristic period of inconsistency since a shock third-round exit from Wimbledon last July.

The Serbian lost top spot in the world rankings to Andy Murray in November, parted company with Boris Becker the following month and dismissed his remaining coaching staff in May.

The 12-time grand slam winner began working with Agassi during the lead-up to this event, where he has forged an uncertain path to the last eight, needing five sets to get past Diego Schwartzman and failing to convince early on against Albert Ramos-Vinolas on Sunday.

Despite the contrasting fortunes of the two heavyweights so far in the French capital, Agassi, who is unable to coach Djokovic during the second week of the competition due to a prior commitment, has faith in his superstar pupil. 

"Coming into the tournament, Nadal has been at his best," the American told Omnisport.

"Watching his performance… was incredible. Match-ups are big issues, when he plays the right person he looks better, even. 

"But I've seen Novak do incredible things. I'm not worried about who's playing great, who's not playing great. Because every day is a new day. And that engagement [with the mental process of working on his game] is going to dictate what happens.

"If I was Novak, the hardest part about this tournament would be going to sleep at night, because I would be very excited about getting out on the court and playing the next person. We've just got to get there."

According to Agassi, Djokovic has no need to amend his physical preparation, with any potential improvement likely to take place in his mentality. 

"Physically, I've never seen a body like this," he said.

"The way he moves – if nothing's broken, you don't fix it. [But] he's never been 30 years old before.

"I think he needs inspiration, information and application. I think he's inspired by finding new ways to accomplish his goals and objectives. 

"There is a new way, it's called thinking about the game a little differently, thinking about the balance of your life differently and it's thinking about finding new solutions to – quite honestly – the same problems we all have. 

"Which is the calculation of trying to be the best we can every day, regardless what our circumstance are. Hopefully, I can help him with it."

Djokovic must get past in-form rising star Dominic Thiem to reach a semi-final against Nadal or Pablo Carreno Busta.