Schmeichel believes the man who replaces Ferguson, 66, must be a former United player who has a strong bond with the club - such as Blackburn boss Hughes or Sunderland manager Keane.
"Who replaces Sir Alex is the big question," he told BBC Five Live's Sportsweek.
"It would make sense to talk to Sir Alex and say 'we don't want you to retire but let's do a plan here and bring your successor in'.
"The successor could work with him for a year or even five years. That would bring continuity.
"I would think Mark Hughes or Roy Keane would be right. Paul Ince is doing well at MK Dons and it will be interesting to see what he's doing next year.
"United have reached a point where they are no longer a club but an institution.
"To have someone coming into that institution with totally different ideas will upset what's been going on."