Balotelli joined AC Milan from City for £19million last month.
Of his compatriot, Mancini told the Guardian: "Mario not being here, that must be a big problem for the paparazzi and The Sun.
"City in the next five to 10 years can be the top club in the world. He didn't think about this, he didn't think about his future.
"He's a good guy. He's not 16, true, but 22 is still young and when you're young you make mistakes."