World number one Djokovic -- who is playing on a wild card in the Geneva Open this week before the second Grand Slam of the year begins in Paris -- said if Nadal was in the draw, he could not be ruled out, despite his injury problems and growing competition from a younger generation.
"This year is more open," reigning French Open champion Djokovic told reporters at the Parc des Eaux-Vives grounds in Geneva
"Casper Ruud is surely one of the five players who are candidates to win. You have Alexander Zverev, Andrey Rublev, Stefanos Tsitsipas -- all the players who won a major tournament on this surface this year.
"But when you talk about Roland-Garros and Nadal is there, he is always the biggest favourite for me.
"After everything he has done on the courts at Roland-Garros court, it's normal, respectfully to put him as the biggest favourite.
"Obviously it's a little different with his level of play. But it's Roland-Garros and it's Nadal.
"After that, maybe me, if I feel good, if I play well. At Roland-Garros, and all the Grand Slams, I am a bit of a different player."
Djokovic, who turns 37 on Wednesday, took a wild card to play in Geneva in a bid to rescue an alarming dip in form ahead of his French Open title defence next week.
The 28-man Swiss clay court tournament serves as a final tune-up before Roland-Garros.
The record 24-time Grand Slam champion will arrive in Paris without a title in the season for the first time since 2018, unless he takes the Geneva trophy.
