World number one Nadal, fresh from a record ninth French Open title, was Wimbledon champion in 2008 and 2010 and runner-up in 2006, 2007 and 2010. But his last two visits have been humiliating disasters. (Agencies)
The Spaniard suffered his first ever opening round exit at a Grand Slam in 2013 to Belgian journeyman Steve Darcis who was ranked 135 at the time and has not won a main tour match since.
Twelve months earlier, the world's 100th best player, big-hitting Lukas Rosol put him out in the second round, a defeat which precipitated a seven-month absence from the sport for the man from Mallorca.
The 28-year-old hinted at another Wimbledon letdown in the immediate aftermath of his triumph over Djokovic in the French Open final two weeks ago where he claimed his 14th major.
"I am healthy, that's the most important thing. I hope my knee will have a positive feeling on grass because I felt my knee was better last year on the other surfaces," said Nadal, who has been seeded number two for Wimbledon.
"Grass is always a little bit harder for me after injury. I played Wimbledon in 2012 with my knee injury and I never played another match after. Last year I tried but I was not ready enough to compete. Let's see how are my feelings this year."
Those feelings would not have been boosted by an opening exit on the grass at Halle last week, a straights sets loss to German world number 85, Dustin Brown.
"The match was negative in all ways," lamented Nadal.
World number two Djokovic, who won his only Wimbledon title in 2011 and was runner-up to Andy Murray in 2013, has not played a grasscourt warm-up event since 2010.
The 27-year-old Serb, the top seed for Wimbledon, 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 last six Grand Slam finals.
Murray promoted above Federer
The coaching role of three-time Wimbledon champion Boris Becker has never looked so crucial.
Meanwhile, Murray, having become the first British man since Fred Perry in 1936 to win Wimbledon when he trounced Djokovic in straight sets last year, goes into the tournament with his form also giving cause for concern.
The world number five, 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.
"The difference between this year and last year is that I've played a lot of matches on clay in the last couple of weeks this time," said Murray, who made the semi-finals at the French Open, losing to Nadal.
"Last year I had about a week to 10 days' preparation on grass before Queen's."
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.
"They have been two of my most successful tournaments, so I hope that this title will bring me luck again."
Last year, Federer was knocked out in the second round by Ukraine's world number 116, Sergei Stakhovsky, ending his run of 36 straight Grand Slam quarter-finals.
At the French Open this year, Federer slumped to a fourth round loss to Latvia's Ernests Gulbis -- his earliest Paris exit since 2004.
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.
World number one Nadal, fresh from a record ninth French Open title, was Wimbledon champion in 2008 and 2010 and runner-up in 2006, 2007 and 2010. But his last two visits have been humiliating disasters.