The England number one goalkeeper is currently out of favour at the Etihad Stadium because of high-profile mistakes at the start of the season, with manager Manuel Pellegrini preferring Costel Pantilimon for the Premier League matches.
"Nothing has changed with him," the Daily Star quotes Milner as saying. "Everybody has ups and downs in their careers. Nobody's career goes in one nice straight line, you have peaks and troughs.
"It's not easy when you're in and out of the team, so to perform how he has when called upon is a great credit to him. He will come back stronger, absolutely.
"Not that you need this, and it's not nice for anyone, but it makes you stronger. You learn from them and anything that your career then throws at you going forward, you can deal with it."
Hart has been at City since 2006.