Dein believes that even if Arsenal make an astute choice when they eventually seek a successor to 66-year-old Wenger, whose contract runs out next year, they will face an uncertain time.
"He won't be a difficult to act to follow... he will be an impossible act to follow," Dein said at the Soccerex Global Convention.
"He's been at the club for 20 seasons and every year has been in the Champions League (since 1998-99) so to anyone wanting to change the manager I say to them that the next person is highly unlikely to do that.
"I had the good fortune to have known Arsene for eight years before he became Arsenal manager so knew what he was like.
"The easiest thing is just to change - the hard thing is getting somebody better. Who could you get that is better?"