Hart's errors against Sweden may have been one bad night, or the accumulated toll of too many high-leverage matches.
After leading City to its first Premiership crown in 44 years, Hart was ranked by FoxSports.com as the sixth-best keeper in the world and the second-best keeper in the Prem behind Petr Cech. He is also England's undisputed No. 1 keeper "by a distance" (via teamtalk.com).
As such, City has the classic "nice problem to have" in Hart. He is a transcendent athlete coming into the prime of his career (if he is not there already) at the age of 25. Hart has also played on significant world stages such as the European Championship, Champions League and Europa League (via soccernet.espn.go.com).
While it would be silly to project Hart as England's definitive No. 1 keeper for the 2014 World Cup, he is starting all of their qualifiers these days. Even when England is projected to dispatch its opposition with ease, there is Hart in the starting XI (via the Guardian).
All of this goes to say that Joe Hart is being spread pretty thin these days. And we have not even discussed his work for Manchester City in the Premier League yet.
City has played 11 Premier League matches this season. Hart started all of them. City has played four Champions League matches this season. Hart started all of them. In fact, Hart has started 87 consecutive Premier League fixtures for City since the start of the 2010-2011 season.
Since the August 19 Premier League opener at home to Southampton, Hart has only once had a full week between meaningful matches. More common are the occasions when Hart has to suit up four times in 12 days in Premier League, Champions League and World Cup qualifying (via soccernet.espn.go.com).
Which is what he just did, from November 3 through November 14.
The demand for Hart's services from England, as well as Mancini's apparent fear of letting Costel Pantilimon handle anything but Community Shield and Capital One Cup duty, puts Hart at risk of overuse (via espnfc.com).
Hart has been exceptionally durable in his career, so the fear of injury is probably not the big concern. A dip in form, such as the one Hart exhibited in England's recent friendly with Sweden, is (via the Guardian).
Meanwhile, from week to week in the Premiership, Hart's City teammates face well-rested keepers. City is likely to see Brad Guzan against Aston Villa in its next match. Guzan was not even selected to go to Russia with the United States Men's National Team this week (via Washington Post). Nor was Brad Friedel, Tottenham Hotspur's keeper against City last weekend. Friedel's last international appearance came in 2005 (via ussoccerplayers.com).
Chelsea will unquestionably start Cech, the Czech Republic's No. 1 keeper, against City. Cech likely feels the same fatigue Hart does. The issue is also the same with Everton's Tim Howard, the No. 1 keeper for the United States.
But just because other top-flight keepers carry heavy workloads does not mean that Hart should never have a chance to catch his breath.
Given all the other work he is called on to do, perhaps Mancini should find Hart a day off when City is home to Aston Villa, or home to Reading, or away to Norwich.
In large measure, as Hart goes, so City goes. Burning him out will do neither Hart nor City any good.