Guardiola says he sees opposition teams now attacking them more aggressively.
"Everyone came to the Etihad and stayed back," he said. "The first team I saw man-marking was Neil Warnock at Cardiff. Now everyone does it. Everyone comes here, it doesn't matter, man to man.
"They just jump to Ederson or Stefan (Ortega). You have to adapt, do it better with the ball, otherwise you are not qualifying for the Champions League.
"Our problem is with the ball. This season it is what we have missed.
"If you have the ball and don't pass properly to your mate, everything is so difficult."
Guardiola also set out new targets for City this season.
"There are seasons when there are a lot of difficulties," Guardiola said. "How do you stand up? How do you stay there?
"I remember Jose (Mourinho). I don't know the reality of United but he said many times finishing second in that season was his biggest success. I understand completely."