Real Madrid are one of the best teams in the world right now if not the best. So an experienced club like Manchester City with an experienced manager like Pep Guardiola would not even dare to underestimate a club like Real Madrid. Pep Guardiola once said in an interview that Real Madrid is the team he is most scared to face in the Uefa Champions League because they never give up. They got that mentality in them. So even thinking that Manchester City will be underestimating Real Madrid is pretty silly and funny.
From the start when in the Champions League which has entered a more intense phase it would be ridiculous when there is still one club that underestimates its opponent because it will only make them lose momentum and lose the match because they are too demeaning a club that is being fought against. Likewise for now in the quarter-finals because looking at what is happening right now where the consistency and status of the club and the probability that Madrid has then it is ridiculous when Manchester City underestimates a club like Madrid.
Although we know that last season in the second leg of the semi-final at Etihad stadium must have given Manchester City a good confidence but still it is not a valid reason to consider the current match easy and underestimate Madrid just because of the previous h2h.
Manchester City's momentum is still very much there because they are also defending but there could indeed be a difference where Madrid wins. I think this will be very interesting because seeing the condition of the two clubs now especially in 3 consecutive seasons always meeting in the Champions League then surely this provides a big sensation in a match of 2 giants in their respective domestic leagues.