The 31-year-old has scored just once in the Premier League in the campaign, and has failed to find his form in the Champions League in the Citizens' two matches.
He told reporters: "I don't agree that Yaya has had a bad season. Maybe if you compare his performances this year to last season, when he had a brilliant performance, maybe he just needs time to get back to that level.
"But he continues to be a very important player for our team, especially as he showed two games ago against Aston Villa. He has the quality to make the difference when we have to fight when we play teams who have 10 men behind the ball."
City face CSKA Moscow in their Champions League Group E clash later today.