Fergie, who is preparing his side to face City this weekend, believes title rivals Arsenal are not currently in good shape and that City caught them on a good day last week.
"Maybe City got Arsenal on the right day last Saturday because there seems to be a lot of disarray in the Arsenal camp with the carry-on with one of their players," said Ferguson. But you can only do what you are supposed to do and City did that very convincingly."
Wenger has angrily rejected Ferguson's claims as he looks to get his side back in the title hunt against Chelsea on Sunday.
"I don't feel we are in disarray, I feel that Manchester City are a good side and Manchester United will maybe see that on Sunday. We had a few bad results and with the pace set by Liverpool and Chelsea, that made us drop off, but the quality is there and what happened to us can happen to them. If this team beats Chelsea after having beaten Manchester United, I believe they will go from strength to strength. You just have to believe, and I know we can beat them."