The former Ajax star has battled to settle since his summer arrival.
"I know how they want to play and how they like to play – they like that little one-two, that connection and that, if we can say, 'tiki-taka' football and Donny is one of those guys from the beautiful Ajax football.
"They teach that growing up and they give a lot of good players to the world. If you look at the semi-final they played against Tottenham [in 2018/19], most of the players from that team are playing in big clubs and doing well.
"I hope Donny can do a lot of things for us and I'm sure he will do. Of course though every player has to take time to get settled in the club and I think he is doing well, but he can do much better for us and he also wants to do much better."