The forward left the Premier League champions for the Serie A giants last week, and Neville criticises the Italian international for his conduct at City.
"Balotelli wasn't a maverick, he was an unprofessional footballer," Nevile said in his column in the Daily Mail.
"Fighting with your teammates and manager, getting sent off in crucial games, going out the night before a match and causing a disturbance the evening before a big game are all examples of that.
"There's no doubt he had his moments, some of them excellent. But at Manchester City they weren't delivered consistently enough."
Balotelli was brought to City from Milan's arch-rivals Inter for £24m in 2010.