Tennis legend Stefan Edberg conceded that emulating Roger Federer's achievement of winning 20 Grand Slams is "nearly impossible" but has backed Rafael Nadal and Novak Djokovic to catch up, provided they remain fit for the rest of their careers.

Edberg, the six-time Grand Slam champion from Sweden, opined the reigning Australian Open champion is peerless not just in the modern-era but is also a cut above legendary names, including Rod Laver, John McEnroe, and Bjorn Borg.

"Is there another player who could do the same, it's Rafael Nadal, he is still young enough to get up there if he can stay healthy," Edberg told the Press Trust of India.

He added: "And you have Novak Djokovic who has won lot of grand slams, so those are the two players who have a chance to get to 20 Grand Slams but it's a long long way and it is nearly impossible, and apart from that it's going to take another 10-15 years before anybody has a chance to achieve the same."

"Obviously you had Rod Laver going back, who didn't play professional circuit for a number of years, he is one of the legends, I have seen them all play, from McEnroe, Borg on television of course, (but) he [Federer] probably stands out as of now."

'Astonishing tennis player'

Roger Federer
Roger Federer won his third title in Rotterdam earlier this month.KOEN SUYK/AFP/Getty Images
rafael nadal, tennis
Rafael Nadal will make a comeback following his hip injury at this week's Mexican Open in Acapulco.Scott Barbour/Getty

Edberg also expressed surprise at Federer's resurgence over the last two seasons, saying it "is almost impossible" to achieve what the Swiss star has at 36.

Federer became the oldest world number one earlier this month, dethroning arch-rival Nadal from the top of the ATP rankings. He has started the 2018 season on a high, defending his Australian Open crown and winning an ATP 500 title in Rotterdam.

It all began when Federer rallied against the odds and ended his four-year Grand Slam drought at Australian Open 2017. The Swiss legend proved his win in Melbourne was no flash in the pan by dominating the chasing pack. He won his eighth Wimbledon title last year, in which he defeated Nadal four times on the trot.

On the other hand, the likes of former top-ranked stars Djokovic and Andy Murray have been struggling to remain fit. The two, who went head-to-head for the year-ending number one spot in 2016, ended their 2017 seasons early and are yet to achieve full fitness.

"Roger Federer is quite an astonishing tennis player and to reach number one at this stage of (his) career and at this age, it's probably like a dream in many ways, maybe for himself," Edberg said.

"I don't think anybody could have believed that this could have happened. Possibly he would have been happy with one Grand Slam more, but now he has won three in 12 months, it's incredible, it's almost impossible to do what he has done but he has surprised us."