The Citizens have dropped to 15 points behind local rivals Manchester United in the defence of their maiden Premier League title, although they do have a game in hand against Aston Villa on Monday night, a run that has led to criticism coming the way of the manager.
"When I was a player I always took responsibility," Mancini told reporters. "When I didn’t play well, I said: 'Sorry I didn’t play well and will do my best in the next game' and it should be like this.
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"I said that, for me, Samir is a top player and a top player should play well in every game. It's the same for Joe.
"Samir knows this because I have spoken about this situation many times with him. He can do better because he has quality, technique and he’s strong."
Mancini has been derided for his confrontational man-management style, which has seen him fall out with several of the club's players such as Nasri and Hart, as well as Carlos Tevez and the now departed Mario Balotelli.
However, the 48-year-old argued that such honesty was necessary with his squad of players, who he believes have just taken their eye off the ball after their successes in recent years and have allowed United to steal a march on them.
"I’m not rude with my players," he reasoned. "I say what I think sometimes and if I think it could be good for my players to understand they could play better or they can do more.
"Sometimes we haven’t played with the same attitude that we had last year. When you win, like last year, it’s easy. When you have a problem, you should resolve that problem.
"I love all of my players and I can do everything for them, but I want them to do everything for the club.
"Maybe they don’t play better because they think it’s enough to play with only one foot. We won the championship after two years and it’s clear it’s more difficult the year after, but we had the chance."