Rafael Nadal claims the jury is still out on teenage sensation Nick Kyrgios' star quality.

Unflustered Australian Kyrgios blasted past world number one Nadal and into his first Grand Slam quarter-final at Wimbledon on Tuesday.

Second seed Nadal completed a miserable three years at the All England Club in defeat to the world number 144, following a first-round exit in 2013 and second-round slump in 2012.

The 28-year-old admitted wild-card entrant Kyrgios deserved his fourth-round victory, but refused to endorse the Canberra native's bid for prolonged top-10 success.

"This sport is mental a lot of the time," said Nadal, after his 7-6 (7/5) 5-7 7-6 (7/5) 6-3 loss.

"He has things, positive things, to be a good player. But at the end, everything is a little bit easier when you are arriving.

"Everything is new, nothing to lose; everything is good, everything is positive.

"You can do whatever and it will be positive, and everybody will just see the good things in you.

"When you are there yourself, the rest of the people start to see the negative things in your tennis.

"We'll see if he's able to improve and to play at a very high level for a long period of time.

"When we see a young player that arrives on the tour and plays a great match or tournament, people say he will be the next big star.

"Sometimes they are right, sometimes not. It depends how things improve over the next couple of months and years for him.

"If he is able to keep improving he will be there - if not, it will be more difficult. I wish him all the best."

"I created my opportunities, but I was not able to read his serve" - Rafael Nadal

Nadal arrived at Wimbledon fresh from his ninth French Open triumph, but also with a clean bill of health where his troublesome knees were concerned.

The five-time finalist said he was "satisfied" with his 2014 Wimbledon return, pledging to hit the beach in his native Majorca.

"It's true that my draw was not the best, all the matches were uncomfortable against players that didn't give you the opportunity to play a lot," he said.

"I fought until the end in every single match. I was able to play some good tennis on this surface, and that's something I've not been able to do in the last two years.

"In a way I am not even angry today because I lost the match losing my serve only once in the whole match.

"I created my opportunities, but I was not able to read his serve. When you have an opponent who serves that well and hits every ball so hard, you are in trouble.

"I don't think I played badly, but that's the game on this surface. I think in the second and the third set I was better than him, but I was not able to convert opportunities - and for the rest, I think he played better than me.

"In general, talking about what you need to win on this surface, he did those things better than me. Congratulations to him - for me, it's the beach."