Switzerland’s 17-time Grand Slam winner Roger Federer on Monday said he still believed Rafael Nadal was the favourite to win the French Open next month despite the Spanish star’s troubled start to the clay court season.Federer, who took his sole French Open title in 2009, this week is refining his own clay court game at the Istanbul Open, the first ATP World Tour event to be held in Turkey and the first time that Federer has visited the country.But Nadal, who with the exception of Federer’s win has taken every French Open since 2005 to make nine in total, has shown a dip in form over the past weeks, failing to get past the third round at last week’s Barcelona Open. Federer said he believed that Nadal was still the man to beat on the red clay of Roland Garros, along with the in-form Serbian world number one Novak Djokovic. Also Read – Khel Ratna for Deepa and Bajrang, Arjuna for Jadeja“At the French Open, Rafa for me is still the favourite alongside Djokovic who has been playing so well. Even though his (Nadal’s) form is not as good as in previous years, I still believe when the French Open rolls around he is going to be very difficult to beat,” he told a news conference in Istanbul.Federer, 33, is himself looking for his own form on the slower clay after a long hard court season, having lost in the third round to Gael Monfils at the Monte Carlo Masters this month. But he said the Istanbul event was ideal for his preparations. “It’s about getting used to the sliding, deciding how aggressive I want to play,” said the world number two.Federer, who so far has been unable to add to his sole French Open win in 2009 and won his last grand slam at Wimbledon in 2012, acknowledged that this year’s French Open “is clearly a big goal of mine.” “But to play well at the French Open I need confidence. I hope that I can pick that up in Istanbulm,” said the former Swiss world no. 1.