Guardiola, who spent in excess of £160m last summer, feels that his squad are lacking "not in terms of quality" but rather in their "mentality and the presence to play at that level".
The Spaniard told Sky Sports News: "We see in the Champions League that level [that those teams are at] and the quality they have.
"But it is not just the quality, it is the mentality and the presence to play at that level. Of course we have to make changes for next season. It is how they play in big situations. We lived those situations in the Monaco game so we do not forget how good they are.
"We were able to score six goals in two games but we are out. That means it is how you handle the whole situation over 180 minutes. For that you need experience. Hopefully that experience will help us for next season."
Man City, who play Southampton in the Premier League on Saturday, remain in the hunt for a Champions League spot as they sit fourth in the table.