Manchester United manager Sir Alex Ferguson says Manchester City "are a small club with a small mentality".
The Scot is unimpressed by City signing Carlos Tevez when the Argentine left Old Trafford at the end of last season.
A city-centre billboard appeared soon after, saying "Carlos Tevez, welcome to Manchester" under a sky-blue graphic.
"It's City isn't it? They're a small club with a small mentality. All they can talk about is Manchester United; they can't get away from it," he said.
"They think taking Carlos Tevez away from Manchester United is a triumph. It is poor stuff."
Manchester City have spent heavily in recent weeks, with Emmanuel Adebayor signing from Arsenal for about £25m, midfielder Barry coming from Aston Villa for £12m, Paraguayan frontman Santa Cruz costing £18m from Blackburn, and Tevez arriving for £25m.
The billboard poster went up in Manchester after Tevez signed for CityFerguson, who was speaking on the Premier League champions' pre-season tour in China, claimed that Adebayor had attempted to sign for Manchester United before committing to City.
"When someone offers you that kind of money, it is a big attraction," said Ferguson. "That is the reason they have gone there.
"At the last minute, from what I can gather, either Emmanuel Adebayor or his agent phoned us after they had agreed a deal with City and then did the same with Chelsea. He was desperate to get to either Chelsea or us."