United are to mark the Scot's phenomenally successful 26 years in charge at Old Trafford by unveiling a statue of the 70-year-old outside the stand that already bears his name on Friday.
Wenger has had many close duels with Ferguson during his own remarkable 16 years with the Gunners but still holds his old adversary in the highest regard and expects United to struggle to replace him.
The Frenchman said: "I don't remember anybody else being at the top, top level for such a long time.
"In some ways it is scary as well because you think when this guy leaves the club, no matter of 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 that his commitment 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."
Ferguson won the first of his 12 Premier League titles with United in 1993 and has also overseen Champions League success twice. There have also been five FA Cup wins.
Veteran Ryan Giggs, who has been a key member of the first team for most of Ferguson's reign, has also been wholesome in his praise.
The 38-year-old said: "He's just a great man. Even though he is managing the greatest club in the world and the biggest club in the world, he still has time for any young player or any player with problems - both on and off the pitch.
"He's the biggest influence on my career so I can't speak highly enough about him."
England hero David Beckham found stardom under Ferguson and was a member of six title-winning sides before leaving for Real Madrid in 2003.
Beckham may have had his differences with Ferguson at times but the pair have long since been reconciled and the respect is evident.
Beckham said: "I think the manager has been so successful because he's passionate about Manchester United and he's a born winner.
"He knows how to win games, how to handle pressure and how to look after his team and his players.
"Playing under him for the years that I did, well - he was like a father figure to me.
"I moved up from London to Manchester and he always said to me, 'If you've got any worries, come and knock on my door - it's always open'.
"I was scared to go and knock on his door because of who he is but he always made me feel as if I was part of a family and that's how you feel when you're at Manchester United."
Another influential player was defender Gary Neville, who is now on the England coaching staff and forging a promising media career.
Neville said: "To be at this club for so long is staggering. You would never believe it could happen.
"I've said before, United had Sir Matt Busby, now they've got somebody who's replicated his longevity at the club and surpassed his success - you would just never believe it could be achieved.
"It's really not something you can put into words, what Sir Alex Ferguson has done for the club."