Real Madrid performed poorly in La Liga last season but played well in the Champions League, losing to the reigning champions in the semi-finals. So it may happen that this season they may do well in La Liga but poorly in the Champions League. We have to wait for the group stage and see how they perform.
This is still just speculation or personal opinion. I've seen how Real Madrid have played in the three games that have been played in La Liga, they played quite well and managed to get three consecutive wins even though they haven't found the right person to replace Benzema. Real Madrid's best purchase this season Bellingham has played extraordinary, he has scored four goals in three La Liga games. His arrival to Real Madrid has given new hope to the Bernabeu public after they just lost their Legend who had gone to the Arab League.
Real Madrid will focus on the Champions League and also La Liga, Ancelotti is trying to give something of value to Real Madrid as the most beautiful farewell gift at the end of the season.
Of course Real Madrid are called the Royal Club for a reason, so they are always favourites for the title in any cups, and I only said my opinion. But the first three games in La Liga against not the strongest clubs does not mean that Real Madrid are well prepared for the Champions League.