I think the chances of Barcelona losing this match are very slim, because Valencia's performance is very different from Barcelona's. So, with that in mind, I think Barcelona will definitely win this match. Personally, I think the potential for a draw is very small. I'm very confident that Barcelona will win, whether by a large or small score. Barcelona will definitely not repeat the mistakes they made in the previous match.
Barcelona did not start this season well and with likely not too small effects from FIFA days, Barcelona will not have best player resources and best fitness for the match with Valencia. While they no longer want to drop any more point, Valencia are not a too weak team to easily lose this match. Barcelona still relies too much on Rafinha and Lamal in attacks while these players are actually exhausted physically and mentally with latest matches for Spain and Brazil as their international duties.
I really don't think Real Madrid will drop point in that match because they still want to lift the la Liga title this season I believe that they will not drop any of their players they will use them to play the la Liga match between Real sociedad, if they don't have any injury 3 days is enough resting day for the players so I really don't see it as a big deal for them they will use all their best players in that match and still use all the best players in the champions League match and it may turn out well for them however if there players has injury in the match between Real sociedad then it will affect them in the champions League match but I see no reason for them to rest their best players because I believe they won't have any issues or injury after the match with Real sociedad.
Want to win a match and actually win it are sometimes different as win it or not, it depends on your performance which decides the match result. Real Madrid are stronger than Real Sociedad and can win this opponent but it's interesting to see Xabi Alonso facing with Real Sociedad where he was grown up as a young player many years ago. Real Madrid have good chance to win against Real Sociedad but they must be very carefully as no three points come easily especially Real Sociedad is not a too weak club in La Liga.