The Italian coach has faced criticism for switching his defensive tactics midway through City's 3-1 defeat to Ajax in Amsterdam last night.
"If you have spirit you have quality to play Champions League," BBC Sport quotes Mancini as saying. "If not, you can't. This is the problem. It is not important, the tactics. When you play this game you should have good spirit."
City currently sit at the bottom of their group and are unlikely to qualify for the knockout stages of the European competition.