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World No. 1 Rafael Nadal fears he could be the victim of another Wimbledon giant-killing this year.

Nadal continues to trounce all challengers on his favourite claycourts at the French Open, where he was crowned champion for an incredible ninth time earlier this month.

But after reaching the All England Club final five times between 2006 and 2011, the two-time Wimbledon champion has endured a miserable time on grass of late.

Nadal endured a shock loss in the Wimbledon second round against Lukas Rosol in 2012 and was embarrassed by Belgium’s Steve Darcis in the first round last year.

The 28-year-old followed that by suffering his third successive loss on grass when he crashed out of the Wimbledon warm-up in Halle against Dustin Brown earlier this month.

Roger Federer, the seven-time Wimbledon champion, believes Nadal might be vulnerable in the early rounds and the second seeded Spaniard agrees that the transition from the clay to grass with little preparation time makes him nervous.

“I’ve said before this is really the most dangerous tournament of the year,” Nadal told reporters on Saturday.

Andy Murray looks relaxed ahead of his title defence. Photo: Getty

“When I arrive at Roland Garros I already played for one month on clay. I played a lot of matches. So more or less I can imagine how I am going to play. US Open is the same.

“Here, especially the beginning of the tournament, the courts are a little bit faster. The feeling on court is a little bit strange for everybody. Especially the top players who have more pressure.

“Then the match is decided in a few balls, so you need to convert the small opportunities that you have.”

With Rosol lurking as a potential second-round opponent this year, and big-serving Ivo Karlovic another tricky challenger in the third round, Nadal, who starts against Slovakia’s Martin Klizan, knows he has to survive the first week before he will start to believe he can win the tournament.

He has often arrived at Wimbledon struggling with knee and back problems, with the gruelling claycourt campaign aggravating his long-standing issues.

But this year the 14-time Grand Slam winner says he feels in better shape.

“I am able to move myself more freely now. I’m not scared about my knee. That’s the most important thing for me.”

Another former champion, World No.2 Novak Djokovic, is also facing an uphill battle, despite his No. 1 seeding. Djokovic won his only Wimbledon title in 2011 and was runner-up to Andy Murray in 2013, but has not played a grasscourt warm-up event since 2010.

The 27-year-old Serb won the last of his six majors at the Australian Open in 2013.

But his latest thwarted attempt to win a first French Open and become just the eighth man to complete a career grand slam represented his seventh defeat in 13 finals at the majors.

Even more worryingly, Djokovic has now lost five of his past six grand slam finals.

Roger Federer would become the oldest men’s champion should he win. Photo: Getty

The coaching role of three-time Wimbledon champion Boris Becker has never looked so crucial.

Meanwhile, defending champion Murray goes into the tournament with his form also giving cause for concern.

The world No.5, who recently hired Amelie Mauresmo as coach, hasn’t reached another final since and lost in the third round at Queen’s Club last week to 35-year-old Czech, Radek Stepanek.

Murray has been seeded three for Wimbledon, above seven-time champion Roger Federer, who may have most reasons for being confident about an eighth title having captured the Halle grasscourt trophy for the seventh time at the weekend.

The 32-year-old, who won the last of his 17 majors at Wimbledon in 2012, hopes his success in Germany is a sign of good things to come in south-west London.

“In the past, when I have played well at Halle I have usually played well at Wimbledon,” said the Swiss star.

Last year, Federer was knocked out in the second round by Ukraine’s world No.116, Sergei Stakhovsky, ending his run of 36 straight grand slam quarter-finals.

Should he triumph in London Federer would succeed Arthur Ashe as the oldest men’s champion and break free of his seven-title tie with Pete Sampras.

AAP