The world number one, without a title this year, accepted a wildcard for Geneva as he seeks to gain confidence on clay ahead of Roland-Garros. After going out in the semi-finals of the Monte Carlo Masters to Casper Ruud, Djokovic suffered a shock third-round exit at the Italian Open to Chile's Alejandro Tabilo. That latest defeat came a couple of days after the 24-time Grand Slam winner was struck by a bottle while signing autographs.

Ruud is also taking the unusual step of playing the week before a Slam in Geneva, while 14-time French Open champion Rafael Nadal has failed to reach the quarter-finals in three clay-court events this year.

On Tuesday, when asked about who were the likely contenders at the French Open, Djokovic said, "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, 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."

As for his own chances, the Serbian star commented, "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."

On his decision to play in Geneva, Djokovic replied, "I'm searching for my highest possible level. It's not an obligation. It's truly my desire, my feeling, my passion, my love for tennis. That's the most important. I'm seeking to stay connected with that feeling.

"At this moment, there is no better practice for me than match play. So I feel like I need more matches. That's the way for me to try to find the kind of form that I need for Roland-Garros."

Djokovic will hope to celebrate his 37th birthday on Wednesday with a win over German Yannick Hanfmann in Geneva. The French Open starts on Sunday.