"Nobody can take a team and immediately bring first position," said Juventus boss Ranieri, who was in charge at Chelsea for four seasons in all.
"I think given this year, another year and a third year - Sven would get the team in the first four."
Asked if he thinks it would be a mistake for City to sack Eriksson, Ranieri said: "I think so."
He added: "The first year it is very difficult to immediately field a good team.
"The Premiership is very hard and there are a lot of good teams."