The Swans produced a spirited performance against City at the Liberty Stadium but eventually lost 2-1 to be dumped out of the competition.
"I am a little bit disappointed because I think we deserve another result after 90 minutes," Guidolin said.
"We deserved to draw. The game was balanced. The performance of my team for me was good, in the first half and the second half.
"But it's not a good moment for us. Sometimes little things go against you and in this case it was a deflection on the first goal."