If Barca win their group, and Atletico wins theirs, Real will be in a position to choose. In that case, if Real win the group, they'll risk getting Bayern or City. If they end up 2nd, they'll get one of Arsenal(PSG), Napoli(Benfica), Monaco, Leicester or Juve.
It will depend on Atletico's result against Bayern in Munich, but if Atletico won't lose by 2 or more, then I think that Real won't mind finishing 2nd in their group. Real will play 1 day after Bayern-Atletico.