Nadal, who turned 33 this month, has opted not to play any competitive tournaments on grass ahead of the Championships, practising instead at home on grass in Mallorca.
He lacked sharpness at the Hurlingham Club in London as a well-drilled Cilic sent him packing in less than an hour -- a sweating Nadal going straight from court to a waiting black Rolls Royce and away minutes after his 6-3 6-3 defeat.
"This was the first time that I played points and that was too much for me today," Nadal, who won a record-extending 12th French Open title earlier this month, said on court at the Aspall Tennis Classic alongside the Thames.
"I'm excited to be back at Wimbledon. This type of match today helps to try to be ready. Of course I decided not to play a tournament before Wimbledon, I'm 33 so I need to save energy.
"I will just try to improve a little bit every single day and on Friday I have will try to be a bit better."
Nadal, who won Wimbledon in 2008 and 2010, reached the semi-final last year at the All England Club but had struggled in his previous five appearances at the event.
That was reflected in Wednesday's seedings which put Nadal, the world number two, at three, behind eight-time champion Roger Federer who was bumped up one place from his ranking.
Cilic benefited from Wimbledon's unique seeding system and will be 13th -- up five from his ATP ranking of 18.
While Wednesday's match was not an official one he showed exactly why he will be a threat with his hefty serve and forehand giving Nadal little opportunity to get his teeth into any rallies longer than three or four strokes.
Nadal has been critical of Wimbledon's seeding reflecting grasscourt results for the past two years, but Cilic, runner-up in 2017, was certainly not complaining.
"I think they have been doing it for years," he told Reuters. "I've moved into the 13 to 16 group so that definitely helps me avoid higher seeds before the fourth round.
"There are positives and negatives about it. The grass is not as it was in the past when the claycourters struggled to go through one or two rounds at Wimbledon, it's more playable.
"If you see the top 32 these days they all play well on every surface so I guess you could just stay with the rankings."
Nadal will practise at Wimbledon on Thursday before returning to Hurlingham for another match on Friday.
(Reporting by Martyn Herman; Editing by Christian Radnedge)
