As the most prestigious club competition in the whole of Europe, the UEFA Champions League competition isn't a league where any team can relax and feel that they'll be undefeatable probably because they're currently running on a good form because until the final winner of the competition is confirmed, there's every possiblity that the least expected team can surprise everyone and lift the trophy.
This has already occurred in some of the league's group stage matches thus far. Small teams overcoming larger ones and triumphing over them when we least expect it. Nobody is unbeatable in this competition, which is why it is known as the League of Champions. The best of the best from each European league compete in this competition to find the best club.
Real Madrid are currently one of the best clubs in the competition and are also the competition's most successful club but if they don't continue to play in their current form or probably improve their performance this season, they might not even make it to the semi finals.
I believe in Real Madrid in this year's Champions League, and what they've shown so far indicates that they will go far in this competition, as they always do. They are among the top teams with a potential to win this competition this season but will still be based on their consistency in the league.