The 19-year-old Australian stunned the tennis world with a four-set victory over the world number one today, booking his place in the last eight at SW19 in the process.
"This sport is mental a lot of the time. He has things, positive things, to be a good player. But at the end, everything is a little bit easier when you are arriving," Nadal told reporters.
"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."
Kyrgios will face Milos Raonic in the quarter-finals of Wimbledon.