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 today.
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!"
He went on: "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 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.
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.
He 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."
Another influential player was defender Gary Neville, who is now on the England coaching staff and forging a promising media career.
Neville said: "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."