His agent admits that it is unlikely that Paul Ince will agree to release the player, so any interested party must be prepared to pay a fee.
Lens went on to confirm that he is yet to receive a formal approach from any Dutch club.
"The ball lies in their court," he added. "If AZ make their interest official, then Blackburn will have to make a decision.
"When there was interest in the winter Rovers were very clear that they would not sell.
"That's why I don't imagine it will be easy now, because Andre is an important player."
Lens continued: "He doesn't have to leave anyway.
"But he is very interested in the possibilities available at AZ. He is very positive about that.
"The big question is if Blackburn will allow him to talk with them. If not, nothing happens."