Yaya Touré’s personal problems are affecting his form, Manuel Pellegrini has admitted, and the Manchester City manager called on fans to support the midfielder rather than criticise him.

Touré was a disappointment in City’s 1-0 defeat to Bayern Munich in the opening Champions League group match on Wednesday and some fans voiced their disquiet at the 31-year-old on social media. Pellegrini, though, explained that the midfielder is still suffering as a result of the loss of his brother Ibrahim, who died of cancer in June.

“I think that Yaya is a player that makes a difference in big games,” said the manager, when asked if Touré can impress against elite teams as he will be asked to do in Sunday’s visit of Chelsea. “Maybe some of you think it’s strange why he is not in the best moment but we started the season and maybe he had a lot of personal problems with his brother, not what was said in the media, but in what he feels about it and there are a lot of human things. Maybe that is why he is not in his best performance at the moment.

“I think as a team, as a coach, as a club we must support him because he is a very important player, he makes a difference and I’m sure he will return to his best. But he is always being criticised. Yaya, in the last season when he was in his best moment, he always received criticism about how he plays. It is very easy to say he should score 20 goals but must also defend and have better pace and a lot of things that Yaya always received maybe because the way he plays. I don’t think Yaya has any problem.”

Pellegrini shrugged off the question of whether Touré requires both Fernandinho and Fernando to provide defensive ballast so that he can be freed up to attack more. “I don’t think this team depends on one player,” he said. “Last year we didn’t have one player [Fernando], we played well with Fernandinho and Yaya. As a manager I never have an excuse because we don’t have one player. Why do you want to change Yaya into another position? He was the best player in that position last year and you want to change his position? Maybe there will be a possibility to play in some way with Yaya, Fernando and Fernandinho, because Yaya can play in both positions. But I’m not waiting for Fernando to change Yaya’s position.

“You saw Yaya play last season: that is his best position. He was the best player playing in the position that he likes and makes a difference.”

Pellegrini would not reveal whether he would remove Touré from the side if he needed some time to refocus. “What I think about the players I talk with the players personally,” he said.

Eliaquim Mangala, signed for £32m, is yet to make an appearance despite the season being six weeks old. Pellegrini admitted that this is partly because the French central defender has not yet adjusted to the side’s system. “He needs some time to understand the way we defend,” said the 61-year-old. “He is ready and maybe he will be involved soon in our team.

“The other important reason is that I think Kompany and Demichelis are in a very good moment. They are defending very well and that is why for the moment he is not playing. We have to make rotation, we have a lot of games so we are very happy with Mangala and there is no problem with him. The competition is very good but not only is this about the competition why he doesn’t play. I repeat he must know the way we defend as it is not similar to other teams”

If City lose to Chelsea, José Mourinho’s team will leap eight points ahead of the champions. “I always try to think of positives so I hope we are not going to lose and we are not going to go eight points behind Chelsea,” Pellegrini said. “It is better for you to ask me the question after the game. You can ask me what would you think if you are just two points behind Chelsea.”

Stevan Jovetic’s injury leaves City with only Sergio Agüero and Edin Dzeko up front and the latter is a doubt for Chelsea with a back problem, but Pellegrini denied that sending Álvaro Negredo on loan to Valencia was a risk. “It is important to be clear about it,” he said. “We cannot miss Negredo because he can’t play. We cannot be concerned because if he was here he cannot play. We have restriction with Uefa at the moment. We cannot sign an expensive player and leave him out of the Champions League list.

“There are important reasons why we stay with this squad and in this moment Stevan is injured and, of course, we have just two strikers but don’t add Agüero because he is fit. He does not have a problem. In this moment we have the squad we need and we will see what will happen until January. In this moment I’m not concerned.”