Van der Sar is set to retire at the end of the season and United have been linked with a host of goalkeepers around Europe in recent months.
Ferguson said: “I hope it’s not impossible because we had a similar situation with Peter Schmeichel when he left and I had the opportunity to sign Edwin then but the situation conspired against us.
“We made the wrong decision but, since we’ve had him, he’s been unbelievable.”
