I agree with this, playing with key players absent usually makes the game feel like it's not been played well enough and some persons who happens to be a fan to a particular player definitely to enjoy a game seeing that their favorite player is injured and isn't playing. Sometimes some persons usually don't seem to completely accept the results in the mind that the game wasn't played by the full squad.

But if they had all the team players completely playing in the squad, then they would be able to say that they are going to accept the results gotten from the game that was played but any other thing short of that is usually not fully accepted by them and in the case of Manchester city and Real Madrid, firstly at the end of the two fixtures home and away, one of the teams will no longer be seen in the champions league this season and this is regardless of the fact they are playing with a complete squad or not what will matter is the results in the end of the game, both team will seem to have equal share of the effects of injury on key player.

For Madrid they aren't certain about their keeper and so does Manchester city with some of their players so somehow I feel they are even and shouldn't be seen like any has got an advantage over the other or any is suffering more injures and is excuse enough, they both have an injury point in their squad and who ever uses that of their opponent best against them then gets the advantage that will keep them ahead.