San Lorenzo coach Simeone played for Mancini with Lazio.
"I would warn the Manchester City players that Mancini is very rigorous and serious in his work," he told the Daily Mail.
"Any player who does not buy in to the work rate and the spirit of the team will be out, without a doubt.
"These things are important to him. He is very open with his players but he is also very clear. He believes in team unity above anything else. He thinks that is the way to be successful. The players he has there at City will have to understand that.
"My experiences of Mancini were positive. He is not a typical Italian coach. He will not use a typically defensive Italian system and so for a player like Robinho or Carlos Tevez the way he sets the team up could be advantageous.
"But if they are not prepared to work, in both halves of the field, then they won’t be in the team."