Real Madrid must be able to overcome Salzburg first at the Santiago Bernabeu before playing away to Brest. It makes sense, although this is just a personal opinion, but I think Brest was very lucky in the last few games because they got slightly weaker opponents.
This match is very important for Real Madrid to determine their fate in the UCL, so they will play with high spirits to maintain their chances of qualifying through the Play-offs.
Madrid this season is not in the best condition and form in both La Liga and UCL, so indeed we cannot say that Salzburg will be an easy opponent for them, although so far Salzburg has also shown poor performance and consistency in the UCL, but they will certainly come with high spirits to give resistance or at least aim for a draw at the Santiago Bernabeu later.
Regarding Brest, although they may benefit from weaker opponents in recent matches, Madrid still need to focus and not take it lightly, because after all they have shown great consistency to be in the top 7 at the moment.
Brest and Salzburg are not big teams so far, but this season we also seen Madrid have lost to teams that are actually below their quality both in La Liga and UCL, so all possibilities can still happen including Madrid's failure to win in the remaining two matches in UCL this season.