"They are different players", the Dutchman said.
"Defensively, Aaron [Wan-Bissaka] is unbelievable, better than Trent [Alexander-Arnold].
"Yes, Trent has got his attacking and his corners, his right foot. But if you ask Wilf [Zaha] who he would want to play against, every other day, Trent or Wan-Bissaka, I think he will say Trent.
"I have got respect for Trent, because he does everything with his assists and he is great, but defensively, just ask [Raheem] Sterling how good [Aaron] Wan-Bissaka is. It is a problem, and he will switch.
"He is one of the best right-backs, I think he could be, his attacking is good, but he needs more goals or assists to his name.
"Defending comes first, but in the modern game, you need to attack, and at United, you get more of the ball, so go forward and show what you have got, but he has been doing good."