The City boss has bemoaned his team's failure to take more of their chances throughout the current campaign.
City have still scored 89 goals from 43 games this season but, on a number of occasions, missed opportunities have proved costly.
This was evident in their thrilling 1-1 draw with Liverpool a fortnight ago and, even more obviously, in last month's Champions League exit in Monaco.
Defensive issues also contributed to that European defeat on away goals, which came after a 6-6 aggregate draw, but it is up front that Guardiola is most concerned.
Guardiola said: "We have had a lot of chances but we were not able (to score). I don't like to say we were unlucky - we were not good enough. It is simple like that. That has been a big problem for the season.
"We created more chances than Monaco. In the first half we didn't shoot but in the second half we created five clear chances. In Europe you cannot do that - you are out. In many games it was like this.
"We have a specific quality to create the amount of chances but we are not solid enough when we don't score goals. Until now, if you ask me about what I think about the season it is like this, in the boxes we are not good enough.
"We have to improve for next season to compete with good teams in Europe."
It seems likely Guardiola will oversee a reshaping of the squad in the summer to launch a stronger push for trophies next season. Six senior players are out of contract while there is uncertainty over the futures of a number of others, including five who are out on loan.
Read the full article on eurosport.co.uk: Manchester City boss Pep Guardiola wants more goals next season