The Nigerian striker is hoping to play his 20th league game of the season for Newcastle on Saturday against the defending champions
The Nigerian striker who missed out on the Africa Cup of Nations because of his commitment to club said City will be up for the game as they have not performed well of late.
City are 15 points behind United and mathematically must win their remaining nine games and hope their neighbours falter to retain the league crown.
"Sometimes when a sleeping giant has been knocked off its perch, they can be difficult to match," Ameobi told Sky Sports.
"We know that, regardless of what team they put out, regardless of their form, they have the quality to beat anyone.
"We're just hoping that we're at the top of our game, and they're not quite there."
Ameobi has played 19 games this season with just one goal to show.
Newcastle are into the Europa League quarter final and though they are currently in 13th place, they are hoping to finish as high up the league table as possible to have another taste of the competition next season.