Novak Djokovic on Tuesday said Rafael Nadal was his favourite to win the French Open, despite the record 14-time champion struggling for fitness in the twilight of his career. World number one Djokovic is tuning up at the Geneva Open this week before the second Grand Slam of the year begins in Paris. He said if Nadal was in the French Open draw, he could not be ruled out, despite his injury problems and growing competition from a younger generation. "This year is more open," French Open defending 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.