Rafael Nadal's sensational form during the clay-court season means he is the man to beat at the French Open, says defending champion Novak Djokovic.

Nadal, dubbed the 'King of Clay', dropped just two sets from 15 matches as he clinched successive titles in Monte Carlo, Barcelona and Madrid.

His run came to an end at the Internazionali BNL d'Italia in the quarter-finals against Dominic Thiem in the last eight.

But former world number one Djokovic says that Nadal, who starts his quest for a 10th title in Roland Garros, believes that his rival will take some stopping in Paris.

"Rafa, next to Roger [Federer], has been the best player so far this year in terms of results," he told a media conference on Friday.

"I mean, their level of tennis that they have performed is quite fantastic. 

"And Rafa, again, playing on his favourite surface won three tournaments in a row, and he is playing confidently and, you know, much better than he was playing last year.

"So I definitely see him as probably number one favourite for this title."

Were Nadal to triumph in the French capital he would become the first player to win one grand slam on 10 occasions but, despite installing him as favourite, Djokovic says there are plenty of other contenders to deny him.

He added: "And then you have Andy [Murray]. Andy obviously, as I have had in the first four, five months, had a lot of ups and downs with the results. He's still trying to find his right game and consistency.

"Stan [Wawrinka], as well, had a great start to the season, and then he struggled a bit. But, you know, all these guys have won grand slams before. 

"You know, Stan is a big-match player. He always plays his very best when he needs it the most. Andy, as well.

"Dominic Thiem is now someone who alongside with [Alexander] Zverev, who is in great form and who can definitely go far in the tournament.

"It's definitely an interesting edition of 2017 Roland Garros and we will see. It's a long two weeks."