There is a big problem in that game. Atletico is not Manchester City man. They are better than Manchester City and with the way they are playing they might be the team to eliminated Real Madrid from the competition. Sometimes i get to pity for Real Madrid because they have faced stronger opponents than most of the team currently in the UCL. Even in difficult stages they get to play a very strong competitor.
If course there will be a big problem in the game but that will be if Atletico Madrid plays at their best, it will not be easy for Real Madrid not because it is the champions league or because Atletico Madrid is performing well this season but because it is a derby match and this fixture as always been know to be a very strong and competitive gam. Manchester City are not in good shape so it was easy for Madrid to win them but it will not be the same with Atletico Madrid. It will be a very tough match and a difficult one to predict but we all know how good Real Madrid is when it comes to the champions league so we cannot rule them out because Atletico Madrid are better this season.
One thing you failed to understand is that real Madrid don't used to joke with champions league assuming is any other leagues it would have been a different thing,they have proven this so many times even with Manchester city when they were in good form.To me whether Atletico Madrid are in good form or not this season, real Madrid is not a club to joke with morespecially when champions league is concerned they will give all there best to make sure that they defeat Atletico Madrid