These two defenders are in very crucial positions at Manchester City, Stones may still be anticipated, but Walker position so far will make it difficult to find a replacement option. This is clearly a big loss for Manchester City who will face Arsenal and afterwards in the UCL against Madrid. But I don't know yet how long this absence will take, if for 3 to 4 weeks we can't strengthen the Manchester City team, we will face serious problems. We'll see what Pep Guardiola will do to overcome his back line, because for Arsenal this gap is very profitable for them.
As for Real Madrid, they look more prepared for the champions league encounter with Manchester City but that not withstanding, it's a great game to watch between these two giants in the champions league quarter finals stage.
The intensity of the match will be like the peak of the final, Madrid and Manchester City will definitely use all their energy in this match to steal safe points in the first leg. In the last meeting, Manchester City dominated so much that for Madrid this match is a revenge mission.