Van de Beek was left on the bench for Saturday's 0-0 draw with Chelsea.
Ahead of their Champions League clash with RB Leipzig, the manager said: "When players come into a new team, a new league it's always going to be a time that he adapts.
"When Donny has played, he's played really well. It says a lot about our depth of quality in the squad that we don't have to use him every game. It also says everything about our ambitions.
"Donny is going to play a big big part this year. I know at the moment the topic is Donny van de Beek.
"It's nice for some players and commentators to have a little go, but you have to know that you don't have to start the first three games to be a very important player in the squad. He's going to be important, don't worry about that."