"They are top of the league, playing great - as well as they've performed in years," said the striker.
"They obviously beat us quite well in the league and deserved to win that game. But it was only a few weeks earlier that we played really well and beat them in the Community Shield.
"Everyone then was taking a step back then and saying, 'It might be a year too soon for City' and it just shows how quickly things can change.
"They're on a crest of a wave at the minute, but every team will go through a sticky patch at some point and we're still early on in the season.
"We'll see what happens after Christmas and start forming opinions then, but there's no doubt about it, they're a force to be reckoned with."