Johnson spent two-and-a-half seasons at the Etihad Stadium before leaving in the summer after his first-team opportunities became limited to substitute appearances.
The 25-year-old England international now believes players should think about the likelihood of them being involved in manager Roberto Mancini's first team if the opportunity to join City arises.
He told several morning newspapers: "Now, if I was a young lad, I wouldn't go to City.
"It is excellent when a club like City come for you. Hard to turn down. But you don't actually play for the champions - you're a squad member, which is totally different.
"It's not that you're not good enough, it's just that the likes of Yaya Toure are going to play ahead of you, no matter what you do."
Johnson was recruited from Middlesbrough and has FA Cup and Premier League medals to show from his time in Manchester, however he was not involved on the final day of the season when City dramatically beat QPR and missed out on England's Euro 2012 squad.
Johnson was set to line up against City on Saturday as Sunderland headed to Eastlands.
He suspects the large size of the champions' squad, packed with internationals, means some players are bound to develop frustrations if they are not selected regularly by Mancini.
He said: "I think it would only be a matter of time before senior players become unhappy.
"You can probably have too many world-class players at once - everyone wants to play and they're not happy to be squad players.
"You're going to have trouble picking a team, and leaving people in the stands. I was one of them last season.
"He (Mancini) wanted that many players in the squad. He's got to deal with it, hasn't he?"