The Belgian was taken off in their win over Aston Villa on Wednesday night.
It emerged that the midfielder was suffering with a hamstring issue and the City boss has revealed that it is worse than initially feared.
De Bruyne's hamstring tear was reportedly going to keep him out for four weeks.
Now though it could end up being six weeks which would mean City having to deal without their star man.
"It's a big blow, isn't it? It is but we have to move forward," said the Catalan.
"I'm not saying anything that anyone doesn't know, it is unfortunate for him and for us and we have to find a solution because everyone in their own life is struggling in the situation we are living and we have to adapt."