Sir Alex Ferguson's growing dislike of Manchester City manifested itself in another outspoken and wide-ranging attack by the Manchester United manager last night in which he branded them "cocky" and backed the Football Association's decision to ban Emmanuel Adebayor.

At his most provocative, Ferguson also played down City's impressive form this season by describing them as having a "softish start" and he raised the stakes ahead of Sunday's potentially volatile derby at Old Trafford by questioning whether it would have to be regarded as a failure if Mark Hughes, having spent £120m this summer alone, did not win the Premier League this season.

Ferguson described Adebayor's behaviour in City's 4-2 defeat of Arsenal last weekend as "very aggressive" and he made it clear that he was still aggrieved about the manner in which United's neighbours had taunted them after signing Carlos Tevez by putting up a Welcome to Manchester billboard in the city centre.

"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," he said. "They've been a bit, how can I put it, cocky – yes, a bit cocky."

Ferguson was "surprised" City had beaten Arsenal and there was the first sign that he might want to indulge in some mind games with the most prolific spenders in English football. "I think 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 and that's where the difficulty will come for them," he said.

"It's going to be very difficult for them to win the league when you see the likes of ourselves, Liverpool, Chelsea and Arsenal because they've got to beat the four of us at some point this season 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 No1."

Ferguson, speaking to Sirius XM Radio in the United States, was asked about Adebayor's stamp on Robin van Persie and the manner in which the striker had celebrated scoring against his former club by running the length of the pitch to goad the Arsenal fans.

United's manager believes it was more serious than when Gary Neville celebrated a goal in front of Liverpool's supporters at Old Trafford in 2006, incurring a £5,000 fine from the FA. Adebayor, according to Ferguson, had left the FA with no choice but to suspend him for violent conduct for the Van Persie challenge, with the possibility of further sanctions to come.

"It was surprising [behaviour]. I couldn't believe it. He was very aggressive, the boy."

Asked what he would do if one of his players had behaved like that, Ferguson said: "I'd take them into a dark room."

City have won all four of their Premier League games going into what Ferguson predicts will be "quite a volatile" match. "They [City] have had a softish start to the season, with two or three easier games," he said.

He was, however, prepared to admit that City would go to Old Trafford in a confident mood. "Their result on Saturday was the one that surprised people because scoring four goals against Arsenal was an emphatic result. So they have had a good start and, when you get a good start, it can galvanise you and give you confidence, and of course they've got all those players now."