It's a big mistake for a team to underestimate its opponent, even if that opponent has a very bad situation, so there is no reason for Real Madrid to try to underestimate Sevilla. In fact, this is a great opportunity for them to get 3 points, by utilizing the weaknesses and situations that Sevilla is now facing.
It's also worth remembering that the competition is fierce, and even a team that wouldn't normally be in second place is now in second place, Girona. This is a real threat to them that they must take seriously.
I don't think Real Madrid will underestimate Sevilla in any form but they will Play better than Sevilla will do based on their current strength and Madrid is have a complete squad currently as their injured players are back and would most like play in this game so Madrid is in their good form currently and can probably play a team as Sevilla well enough.
Sevilla would only have a hard time playing against Madrid because the squad is now even stronger then they were weeks back, altho they will be trying to utilize the home advantage on their side but then Madrid will most likely not be shaken by that, acenlloti has got the best tactics and the player he needs to get a victory for this match, not to underestimate Sevilla but I think Real Madrid will definitely win but it may not be with a big difference probably a 1-2 or 1-3 in favour of Madrid.