The Red Devils cashed in on their prized asset over the summer for a world record fee of ?0million to Real Madrid, a move Wenger has likened to Thierry Henry's exit in 2007.
The Frenchman believes Henry's influence on the Gunners was similar to that of Ronaldo's and that their respective team-mates adjust and adapt their games once such personalities leave.
The Arsenal tactician thinks Emmanuel Adebayor revelled in Henry's absence while Alexander Hleb gained more charisma without the France international in the side.
Wenger believes Ronaldo will be a big loss for United, although he fully expects Ferguson's prospects and young players to help fill the void vacated by the Portugal international, a scenario he calls the 'Thierry Henry' moment.
The Red Devils have made a slightly inauspicious start to the campaign after losing at Burnley and scraping past Birmingham before putting Wigan to the sword last weekend.
Personalities
"Thierry was, in the end, a personality that had a big weight in the team," explained Wenger. "Also no one could refuse to give him the ball so when he left our play sometimes became a bit more diversified.
"Players like Alex Hleb started to gain more charisma and we had Emmanuel Adebayor, but it takes time.
"United have some big personalities in the team. But Ronaldo won Player of the Year and European Player of the Year so suddenly they have a lack of charisma around them and everybody will look at their team differently.
"Ronaldo didn't look as convincing as the year before. Though when you look at the numbers of games he played and the number of goals he scored he was still as efficient as before.
"I believe they will miss him. When a player becomes too strong in a team, others are a little bit isolated or forgotten.
"So when he disappears many of the players turn up because of the way the game goes through different players.
"Yes, you could say this is their Thierry Henry moment."
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