But van Persie believes the preparatory work his squad is doing with boss Louis Van Gaal - who will manage the striker at Old Trafford next season - will leave it well placed to succeed.
"Normally you have more time to develop another system, now we have to make a little step every day. We are in a bit of hurry," he told Voetbal International.
"We only have a few weeks and two friendlies before we play against the best team in the world. In my opinion, Spain is still the best.
"I really believe in this system. When you see how much progress we make every day, that's very positive. I'm not only talking about the training, but also our meetings off the pitch.
"The coach already said that we're taking risks. If every players fulfills his task, this system can be fantastic.
"Within a few days I saw so much progress in our team. We just know what the coach means and that's very nice to see. We really have to connect."
Netherlands will also face Australia and Chile in a tough-looking Group B.