In the aftermath of Hart's midweek error for England against Poland, former Manchester United and Republic of Ireland captain Keane condemned the Manchester City shot-stopper for his 'cockiness' and also called into question his concentration.
However, Mancini has revealed to The Guardian that he has absolutely no concerns about the mentality of the 25-year-old, and has in fact encouraged his goalkeeper to embrace a degree of arrogance.
"Every keeper is like this. It is important because it's different to another position. If you want to be a keeper, you should be cocky. Joe is a good guy, he works very hard, he wants to improve.
"Last week [Wayne] Rooney said on Twitter that Joe is the best keeper in the world but today he is cocky. It is my opinion that Joe is the best keeper in England and one of the best in Europe. Sometimes a keeper can do a mistake but this is normal.
"If you want to be a good keeper, you should be cocky sometimes. Joe is strong enough for this. He knows he is one of the best but he wants to continue to work.
"If you want to be one of the best you have to work hard all the time. Anyone can make a mistake. It is impossible to be perfect."