The former Bayern Munich boss won his first 10 matches in all competitions before seeing his side's faultless record ended in the last week before the international break with a draw against Celtic and defeat to Tottenham Hotspur.
City will look to return to winning ways when they host Everton on Saturday, but Koeman is optimistic of his side's chances of getting something from the game.
"City have been very good - maybe not the last week before international duty - but it is impressive the way they play football," he told reporters.
"I watched them against Borussia Monchengladbach in the Champions League live and it was a good job to see the difference between how they play this season and how they played last season.
"It's difficult to defend against but we have had some good examples of teams getting a good result against City."
Just four points separate Everton and City in the Premier League table ahead of Saturday's match.