De Ligt has been outstanding for Ajax this season.
And Van der Sar admits his former Manchester United manager has been following the midfielder for some time.
He told Studio Voetbal: “Sir Alex Ferguson said two years ago when we played the Europa League final in Stockholm that De Ligt was going to be a very big player.
“We think so too.
“He also deserves it by how he plays, what he shows, how he speaks and the leadership he shows. Whether he is leaving? Well, I’m not sure about that. Preferably not, of course.”