City went down 4-2 after extra-time despite taking the lead twice and Mancini revealed that he believed the visitors earned the win.
“We were unlucky because we had chances but we conceded goals which we made mistakes on and they deserved to go through,” said Mancini.
“I’m disappointed for the result, Aston Villa are a good team but we didn’t play well.
“Our play is not quick, we want to take one touch too many – this is not good.”
City have now conceded 16 goals in eight matches and the boss revealed his disappointment at shipping another four goals.
“Conceding goals is a real problem, we need to work with our defenders because we aren’t defending well at the moment,” said the Italian.
“To play after just 48 hours rest is very difficult – we changed a lot of players but I think that when the situation is like this, we can do nothing but understand our mistakes and think about how we can get back to our best in the future.”
...Roberto Mancini...
Mancini also revealed that he was especially disappointed to go out of the competition because it’s the only domestic trophy that he has yet to win with City.
“It’s the fourth competition but it’s the only one we haven’t won and for this reason we wanted to win – we are so disappointed.”