Robben was sold to Bayern Munich in August and has enjoyed an impressive start to his German career.
Xabi said: "Robben is a very good player one-on-one and he could break a game at any time. He would have been good in meetings such as Milan, but I should think he would've played little, preferring to accept the offer from Bayern Munich."
On missing Cristiano Ronaldo, Xabi added: "Clearly: Cristiano has unique qualities, brings imbalance in one on one and has the ability to score and find something different.
"Clearly, when the results are not good, Cristiano's absence will be debated."