Real Madrid will most likely be alright eventually, but I think there is a chance that they will lose the next two Champions League games against Liverpool and Atalanta. Both games will be hard to win and if they only get 1 or 2 points from these games, I think it is possible that they will have to go through the play-offs and that could become quite problematic as they are not the only top team who may be forced to go for an extra qualification round. So many big names that there is a strong incentive to get into the top 8.
Being in 18th position with 6 points makes Real Madrid have to work harder to qualify for the last 16 of the Champions League, especially since the opponents they will face next are still very difficult to beat, especially when facing Liverpool. The reason is that Liverpool themselves are in very good condition now so their chances of winning when facing Real Madrid are quite large. It seems that they do have to go through the play-off round to qualify for the last 16 and that is if they can manage to maintain a safe position between 9th and 24th positions in the standings. Ancelotti must be able to ensure that they will still go to the last 16 after 4 remaining matches.