The 22-year-old joined City from Middlesbrough in an £8million deal from Middlesbrough on January transfer window deadline day.
“Johnson is a great player,” said the City boss. “If he continues like he is at the moment he could get into the national team.
“I remember Ryan Giggs when he was young and the way he moved. Johnson is the same player.
“If he keeps working hard he has a good chance for the future.”