The Dutchman spent two years at Real in the 1980s.
Metgod told AS: “The Diarra of Madrid is a very strong guy. Lassana is very small and plays the ball well.
“He passes well both long and short and has very good vision. He is very intelligent and knows very well how he has to play.
“He is very technical. He uses the ball very well and he doesn’t lose it much. He is going to be the player who remains very close to the centre-backs.
“Him, next to Sneijder and Guti, will form a great central midfield.
“Madrid have not made a mistake with him, although you have to recognise that he is not like Van der Vaart or Sneijder, who are always looking to score.”