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.
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."