United wrapped up the title last week, with many suggesting that the Dutchman has been the difference between them and the rest.
Wenger, though, says that United would have won it last year had Queens Park Rangers not realised that they were safe, although he admits that Van Persie has had an impact.
"United have won 20 championships, and they won a few without Robin van Persie," Wenger said. "The difference is that City have dropped off.
"Robin has made an impact of course, I don't deny that, but United lost only on goal difference last year. And if QPR did not know they were safe, [United] would have won it last year."
Arsenal face United at the Emirates Stadium this afternoon, and Wenger confirmed that they will give the champions a guard of honour.