"When I talk with Ryan, I always mention the likes of van Persie, Bergkamp and Robben, players that came from Holland, about how much time they needed to be successful here, maybe one or two years," Benitez told liverpoolfc.tv.
"He was playing at Ajax in a specific role and now he is in a top side in England and everything is different for him. I'm really pleased with his commitment. He is practising everything, learning and trying to improve. I think he will be a very good player for us.
"It's too soon to judge him. It's the same with Lucas Leiva. He's another young player and will need time. We have a reserve team with young players of quality, because we want to give them time."
Benitez added: "Sometimes, with some players, they are so good they can't be kept in the reserves and must go straight to the first team. We know that they will need time, but I'm really pleased with Ryan.
"I think he will be really good. He has all the qualities, he has pace and ability. He'll need to play some games in a row and show good things, that will give him more confidence.
"When you have a young player with quality, if you don't get them into a club as soon as possible, you know they'll sign for another top side.
"You must bring them here and then give them time. We signed Daniel Agger as a young player and after his first six months people were saying they weren't sure about him, then a year later he was one of the best players in our team."