Hart has made just one appearance for City in their last nine matches in all competitions, with Romanian Costel Pantilimon being favoured by manager Manuel Pellegrini.
And Juventus shot-stopper Buffon, who will likely line up for Italy against England when the two sides meet in their World Cup opener in Manaus on June 14, believes it is vital that Hart regains his place in the City starting XI if he is to remain in Roy Hodgson's plans.
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"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," Buffon told the Mail on Sunday.
"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 not playing 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.
"As soon as he [Hart] can start playing regularly again, in my opinion, he can go back to playing as well as he did before, if not better."
Regardless of who plays for England against Italy, Buffon is confident Cesare Prandelli's men will have the psychological advantage in their World Cup meeting.
"We [Italy] are competition animals," he added. "However we play in between tournaments, we always come good in the tournaments themselves.
"It doesn't matter that we're not quite where we want to be right now, in terms of our recent form. You will see the best of Italy by the time we kick off at the World Cup."