Hart was relegated to the bench for Saturday's 7-0 mauling of Norwich in the Premier League after several costly mistakes so far this season in goal for City.
His replacement, Costel Pantilimon, had very little to do in the big win and the Romanian is likely to retain his place in goal ahead of Hart for Tuesday's Champions League tie against CSKA Moscow.
Fernandinho says Hart being dropped proves how good the Premier League is in terms of quality and the England international must work hard to rediscover his best form and earn a recall.
The Brazilian said: "If the quality is a bit off you must work harder to recover your position and your best quality. If he at the moment is not (at his best), he must work more hard.
"But they are very good keepers, he and Pantilimon. I think his career will be better for it.
"The manager must choose the best team, and the best keeper for the team.
"I am sure if he played Joe Hart or Costel Pantilimon the team would be superb because they are both very good goalkeepers."
Man City last week