(CNN) -- Injury is the biggest obstacle standing between Rafael Nadal and a record-extending eighth French Open title, according to former grand slam champion Pat Cash.
The Spaniard is competing at one of tennis' four grand slams for the first time since last year's Wimbledon after spending seven months out of the sport with a knee injury.
The 11-time grand slam champion survived a scare in his opener at Roland Garros before bouncing back to beat unseeded German Daniel Brands in four sets.
Cash, who clinched the Wimbledon title in 1987, reckons the right knee injury which kept Nadal off the court is the biggest threat to his challenge in Paris.
"Nadal is the most incredible clay court player of modern times," said the CNN Open Court presenter. "I think the only question is how fit he is.
"He certainly looks fit and he's hitting the ball unbelievably well.
"Whether his knees will hold up if he gets stuck in a couple of five-set matches, he's going to have tough matches at the French Open there's no doubt about that.
"He's proven over his career that he can do it. He's having such a long clay-court season that his fitness shouldn't be a problem. It's hard not to put him favorite."
Nadal defeated world No. 1 Novak Djokovic in last year's final to clinch an Open-era record seventh French Open title.
The clay-court crown is the only grand slam missing from Djokovic's CV and cash argues the Serb is still short of rivaling Nadal on the surface.
"On clay, Djokovic has his off days, he's more up and down on clay than Nadal is," Cash said of the six-time grand slam winner, who notched up a straight-sets win over Belgium's David Goffin in the first round.
"It makes it much more of a challenge having Nadal there."
One man hoping to challenge for the title is Roger Federer, who eased into the third round Wednesday following a 6-2 6-1 6-1 win over Indian qualifier Somdev Devvarman.
Federer, seeded second, cruised to his 56th victory at the tournament, leaving him just two wins behind the record jointly held by Guillermo Vilas and Nicola Pietrangeli.
But Cash believes the 2009 winner, now 31, faces a huge task to claim an 18th major title with age beginning to catch up with him.
"Federer is starting to take quite a lot of time away from the game," said Cash.
"He's played so many matches, he certainly knows how to play. It's just getting enough sharp matches going into a grand slam.
"In the past he's been able to whip through the early rounds. The way Federer plays, his style, he gives players so little time to breath he's able to whip through the lesser players and it keeps him fresh for the big matches.
"As we saw at the Australian Open, it's the one time in his career he's had to play back-to-back five-set matches, which is unbelievable.
"He couldn't get through that, Andy Murray got the better of him. He is going have to start doing that now he's getting a little bit older. There are a lot of ifs and buts, it makes it interesting."
Federer will play home favorite Julien Benneteau in the next round after the Frenchman prevailed 7-6 7-5 5-7 0-6 6-4 against Germany's Tobias Kamke.
France's hopes of a first men's champion in 30 years remained on course with further victories for Jo-Wilfried Tsonga and Gael Monfils.
Tsonga overcame Finland's Jarkko Nieminen 7-6 6-4 6-3 to set up a clash with compatriot Jeremy Chardy, while Monfils battled past Latvia's Ernests Gulbis 6-7 6-4 7-6 6-2 to earn a third round tie with Tommy Robredo.
There were also victories for Serbia's Janko Tipsarevic, Spain's number four seed David Ferrer and Canada's Milos Raonic.
In the women's section, Serena Williams thrashed Caroline Garcia 6-1 6-2 to set up a last-16 clash with Romania's 26th seed Sorana Cristea.
The 15-time grand slam winner has now gone 26 matches without defeat.
Third seed Victoria Azarenka will face 19-year-old German Annika Beck in the next round following a routine win over Elena Vesnina.
Azarenka, who made the last-eight in Paris in both 2009 and 2011, claimed a 6-1 6-4 victory to set up a clash with the 2012 junior champion.
But there was bad news for Caroline Wozniacki, seeded 10th, who was beaten 7-6 6-3 by world number 47 Bojan Jovanovski.