Wenger said: "I don't remember anybody else being at the top level for such a long time.
"In some ways it is scary because when this guy leaves the club, no matter the quality of who comes in after him, it will be a huge hole.
"The club will be destabilised even if the guy who comes after him is top quality because the print of everything, the life of everything, revolves around Ferguson so much at Manchester United.
"He has to be immortal so the club doesn't suffer! His commitment is always there, you never feel it is weakened.
"What I admire maybe the most in him is his forward-thinking. He is always ready to move with the times and never speaks about what he has done before.
"He knows when to renew the team, when you have to make changes, and that is exceptional because you can sometimes be a little bit lazy when you have so much success.
"He's never been like that, he's always on his toes and he can renew what is needed, when it is needed.
"It is a job where you need to dedicate your life to football and Ferguson has done that and that deserves massive respect.
"He has won absolutely everything and, of course, that is something exceptional."