Costel Pantilimon has been the first-choice keeper for City in recent weeks, and Buffon believes that Hart must be playing regular football in order to keep his spot as England's number one.
"There is usually an order in which you do these things; you normally play for your club and then you play for your national team," he told the Daily Mail.
"To try to play for your national team when you're not playing for your club will become a struggle in the end.
"A player such as Iker Casillas can do it (play for Spain despite being frozen out at Real Madrid) because he has great experience of victory and incredible value as a goalkeeper. But they are very few, those who could succeed in playing for their national team while not playing for their club."
Buffon has won 138 caps for the Italian national team.