Losing in La Liga is not a serious problem for Madrid.
Not a serious problem, what do you mean?
Real Madrid have failed in their La Liga title race this season which is a major setback for the side that dominated La Liga last season. It is clear to me that this is a very serious matter even if Real Madrid win the Copa Del Rey.
Not only that, just look at how weak Real Madrid's defense has been this season compared to last season where I think we've had a bad season so far in La Liga. Conceding 32 goals in 33 matches is not unusual for Real Madrid in the last 4 seasons, but this season Real Madrid have had to admit their weaknesses. There is even a possibility that we will concede more goals if in the next 5 matches Real Madrid form of defense is unable to anticipate the opponent's attacks.
Their coach Carlo Ancelotti after the match also emphasized that his target was to win the Copa del Rey. And he proved successful in presenting the Copa del Rey title to Real Madrid as solace in La Liga. Now Real Madrid are ready to continue their mission in the Champions League and of course they are ready to return to winning ways in La Liga until the end of the season.
The Copa Del Rey is the most realistic target for Real Madrid so they really fought for it, luckily they were able to secure it against Osasuna. Meanwhile, Real Madrid may not win the Champions League, but I will still support them to do it again this season and I'm optimistic about that.