Sir Alex Ferguson believes it would be "foolish" to ignore the threat posed by Manchester City this season.

Ferguson's Manchester United side opened their bid for a record fourth consecutive league title by beating Birmingham 1-0 at Old Trafford yesterday.

Wayne Rooney's first-half effort proved enough to give United maximum points, even if their dominance should have ensured a more comfortable scoreline.

At least it allowed the Red Devils to keep pace with Arsenal and Chelsea, who both started with victories, along with City, who have been the talk of the summer.

"It would be foolish to ignore developments at Eastlands," said Ferguson.

"Manchester City do pose a new threat. We have only to look at how well Chelsea did with back-to-back championships after a massive injection of Russian cash to know money can talk.

"All the leading clubs are looking with interest to see how Mark Hughes handles the situation and whether he can make it work.

"We are all looking over our shoulders, though as far as Manchester United are concerned, it is not in fear."

Indeed, Ferguson feels United will become a more rounded team without Cristiano Ronaldo.

The Portuguese world player of the year was certainly missed yesterday, although only due to the quality of his finishing given United carved out a stack of chances.

Dimitar Berbatov and Michael Owen were both unfortunate not to join Rooney on the scoresheet, with Darren Fletcher also guilty of one poor miss just before the break.

Rooney is the man most Red Devils supporters are looking to fill the gap Ronaldo has left behind.

And Ferguson is confident his star striker can contribute at least 20 goals to the United cause.

"If you have two or three strikers who can get you 20 it stands you in good stead." said Ferguson.

"Wayne Rooney is well capable of that."

There was no argument from Alex McLeish, whose team turned in a creditable performance, without ever quite getting to grips with Rooney's threat.

"We have seen so many natural footballers over the years, people like Zinedine Zidane and Luis Figo, they are difficult to coach.

"You can do one or two things in terms of the shape of the team but when he drops into those little pockets, he is hard to pin down."

Ferguson does have injury problems ahead of Wednesday night's trip to newly-promoted Burnley.

Rio Ferdinand has been ruled out for a fortnight with a thigh injury, Nemanja Vidic is also sidelined, while Jonny Evans is also a major doubt for the trip to Turf Moor after aggravating an ankle injury.

Still, after drawing their last two opening fixtures against teams - Reading and Newcastle - who subsequently got relegated, at least United have three points on the board for what their manager thinks will be the start of an exciting new era.

"I know some of our supporters are still worried that I have not bought a megastar to replace Cristiano," he said.

"They are concerned because they can't quite work out how we are going to compensate for all the goals Cristiano used to get for us.

"But I am more than happy with our squad and although we have lost a major player, I believe we are on the threshold of a very exciting era for Manchester United."