The Swans will play City for the second time in the week at the Liberty Stadium on Saturday after Guidolin's side lost 2-1 to City in the EFL Cup third-round tie on Wednesday.
"I am optimistic because I saw my players play a good game," the Swans boss said.
"At Southampton, we deserved to lose. But in this game we started very well, with focus, aggression, intensity and good ball possession.
"But, as I say, it's not a good moment for us.
"We just have to look forward. If we play well and work hard, I think we are going to have some better moments.
"Saturday against Manchester City will be more difficult than this. They had a very good team tonight even if they played without some players, but on Saturday there will be new important players here.
"But we have to prepare a good game and we have to play well, and then we will see."