The Citizens have been working hard in the transfer market to reinforce their squad after finishing third in the Premier League last season.
City have so far brought in defenders Gael Clichy and Stefan Savic and seemingly striker Sergio Aguero as they look to mount serious challenges on all fronts this season, but David Beckham, who spent 10 years at United, said last week that his former club will always remain dominant in Manchester.
Beckham did state, however, that City are a team to look out for, and Rooney seems to share the same opinion.
"There are at least five or six teams who will compete for the championship this year, among them Manchester City," Rooney told La Gazzetta dello Sport.
"But in the Premier League, more than in any other country, you have to sweat even when you face teams that are at the bottom of the table."Questioned about the clubs he enjoys watching besides his own, Rooney mentioned La Liga's big two, while dedicating special words of praise to Lionel Messi.
"Apart from Manchester, there is no doubt: Real Madrid and Barcelona. They have so many talented players, there is always the chance of a great spectacle," he added.
"The answer [to whom I never get tired of watching] seems obvious: Messi. He has fast feet and is very intelligent. When you see him on the field, everything looks so simple."
Inter's Wesley Sneijder has been strongly linked with a move to Manchester United this summer, but Rooney revealed that his favourite player in Serie A lies elsewhere.
"Before he retired, I was a big fan of [Paolo] Maldini. He was always an example. Now I really appreciate Clarence Seedorf," noted the England international.