Former world No 3 Nikolay Davydenko believes it will hard for Roger Federer and Rafael Nadal to make successful returns from their respective injuries.

Both legends are out for the remainder of the tennis season, with 40-year-old Federer sidelined with a knee injury and 35-year-old Nadal out with a foot injury.

In a recent interview with Eurosport, Davydenko said Federer and Nadal would particularly find the going tough in five-set matches at the Grand Slams.

“I think it will be hard for Rafael Nadal and Roger Federer to return with such injuries,” Davydenko said. “Of course, the fans are going to beat me up now and say I’m talking nonsense. But if you feel it as it is, then they will already give way little by little.

“Maybe they will win something – I’m not saying that they will all lose,” he added. “But I don’t think they can potentially win a five-set match. They can play an hour out of three sets, one and a half. And so you can play a tournament, but the main thing is that if something does not work out again, some kind of injury.”

Davydenko, who won the 2009 ATP Tour Finals by beating Federer and Nadal en route, added it would be tough for the duo to come back from the injuries given their age.

“Roger Federer and Rafael Nadal will go down in the rankings anyway,” Davydenko continued. “They are not playing at all at the moment. I don’t know if they’ll come to the court at all. We are talking about those who are now injured. We do not know when they will come out – we have to ask them.”

Davydenko, who is also 40 and retired in 2014 with 21 career titles, lauded Federer for his longevity but expressed doubt as to whether the Swiss can make another comeback into his 40s.

“Roger Federer has already done everything, reached such heights,” Davydenko said. “He is trying to prove to himself or to someone that he can still win something at the age of 40. But I don’t know what kind of medicines – and medicines are needed for the body to support it and at 40 to be like at 20.

“The difference is big, the body is exhausted, he played so much, moved so much,” the Russian said. “To do this at 40, you cannot win purely by tennis alone.”

Davydenko had a 2-19 losing head-to-head record against Federer, but ended his career with a 6-5 winning record against Nadal.

Photo: Nikolay Davydenko – ATP Tour/Twitter