The Ivorian will be available for the second leg next week but will not feature against Sporting Lisbon in Portugal after picking up two bookings in the last round.
“Yaya is a very important player for us, but we also have another 20 good players and it is important that we give a good performance without him against Sporting,” said Mancini.
“I came here five years ago with Inter Milan in the Champions League and we lost, so I know how hard coming to places like this can be.”
Mancini will also be without the injured Pablo Zabaleta (thigh) while Micah Richards is rated as doubtful ahead of the game.
Sporting, who lost their first match under new coach Ricardo Sa Pinto at the weekend, lie some 11 points off a Champions League berth and have targeted the Europa League as a means to salvaging a disappointing season.
Despite their poor league form, Mancini expects the hosts to be every bit as problematic as Porto were in the previous round.
“All the leading Portuguese sides are strong, especially when they play at home and if you are not at your best, you will lose,” said the City boss.
Sporting don’t lose very often at home, play good football and they also won their Europa League group so we know they are strong, but it is important that we go into the second leg with a good result behind us
...Roberto Mancini
Mancini admitted there is still a lot of hard work ahead if City are to have any chance of winning the Premier League and Europa League, but he believes his squad are capable of what would be a famous double.
“We are here in Portugal with a chance of progressing to the quarter-finals and we are top of the Premier League, but we know it will be difficult to win one or both competitions,” he said.
“There are only two months left of the season and we are where we want to be. I have a very good squad and at this moment, everything is possible and we will be trying to win two trophies.”
