The Dutch striker, who has 20 goals overall for United, snubbed a move to Manchester City, who are seven points behind their neighbours.
Asked whether Van Persie would have had the same effect at the Etihad, Wenger said: "Yes. He is at the peak of his game, 29 going 30. He has gone through difficult moments in his career, he knows his game."
Wenger admits Arsenal's hopes of glory are remote at best - although they have to win tomorrow.
He said: "A win against City would improve the confidence of the team.
"The title looks unlikely but we do not have to give up. We want to fight to come closer and then hope we still have a chance."