Sir Alex Ferguson believes Manchester City have become 'a bit cocky' since their lavish summer spending spree and insists it will be difficult for Mark Hughes' side to win the Premier League title.
City were the top flight's biggest spenders during the transfer window as Hughes snapped up the likes of Emmanuel Adebayor, Kolo Toure and Carlos Tevez for big fees.
Hughes has been rewarded with a 100 per cent start to the season and takes his team to local rivals United on Sunday for one of the most eagerly-awaited derbies in recent years.
United boss Ferguson believes there will now be a greater intensity to the rivalry between the two clubs, but feels City still have a way to go before challenging for the title.
"The rivalry has gone up a notch in the last few months, with them signing all those players and then coming up with that advert and all their posters about Carlos Tevez," Ferguson told American radio station Sirius XM.
"They've been a bit, how can I put it, cocky. Yes, a bit cocky. They've got seven centre-forwards now, which is crazy, just amazing.
"But when you have spent that amount of money, and the wages they are paying, you have to win the league with that kind of investment. That's where the difficulty will come for them.
"It's going to be very difficult for them to win the league when you see ourselves, Liverpool, Chelsea and Arsenal because they've got to beat the four of us at some point to get the league.
"It's very difficult to get into the top four and it's even more difficult to get into the top one - and that's what this league is all about, being No.1."
City have beaten Blackburn, Wolves, Portsmouth and Arsenal to date, but Ferguson said: "They have had a softish start to the season, with two or three easier games."
Adebayor will miss Sunday's clash at Old Trafford after being banned for stamping on Robin van Persie and Ferguson was surprised by the incident.
He said: "It was surprising behaviour. I couldn't believe it. He was very aggressive, the boy."