The Premier League champions will host their Bundesliga counterparts in the Champions League Group D fixture at the Etihad Stadium.
"[Dortmund] are very good on the counter-attack and we expect a very difficult game – it's a really tough group," said the Italian.
"We want to go to the second stage this year so it's important we do well against Dortmund.
"They are probably our main rivals to qualify. But don't forget they only beat Ajax in the last minute."
City lost 3-2 to Spanish champions Real Madrid at the Santiago Bernabeu in their opening group game earlier this month.