Alex has spent the past three seasons on-loan at the Dutch giants, but is expected to join Chelsea this summer.
Cocu told El Mundo Deportivo: “He is a defender of international level. He is very complete, good in the air, very powerful and in one-on-one duels, fast and athletic. He also scores many goals with his long shooting or heading.
“It is really incredible that Chelsea have not wanted to take him until now back to London.”