While I was not expecting to see Barcelona lose this match they lost and even after Yamal got injured he wanted to stay in the team.
Now it seems he is going to be absent in the important match they are going to have with Atletico Mardid, and this can make everything harder for Flick and his players because Atletico Madrid is going to be a much harder competitor for Barcelona than Leganés.

This will be a big disaster for Barcelona, considering that Lamine Yamal is still the backbone of the attack in the front line. Against Atletico Madrid will not be easy, especially since Atletico Madrid has never lost in the last 6 matches in La Liga. This will further motivate Diego Simeone troops to continue to extend their consistency + tickets to the top of the standings.
Barcelona is currently unpredictable and inconsistent. It will be very risky to bet on Barcelona, because they don't have that strength that they started this season with. Atletico Madrid is consistent and very strong which gives them a good hedge over Barcelona. If Barcelona lose this match, it means that they might drop to the thrid position on the table.
With how Barcelona is performing lately in La Liga, I agree with all you said about Barcelona. I was very surprised that Barcelona lost their last match in La Liga at home against Leganes, who has been struggling to win their matches this season in La Liga but traveled to Camp Nou last weekend and beat Barcelona with an early goal from Sergio Gonzalez. It is obvious that Barcelona has lost the energy they started the La Liga season with, and that is the reason why Barcelona is not consistent of late in winning their matches in La Liga. Barcelona's first position in the La Liga table is at risk if they draw or lose against Atlético Madrid, but I don't believe Barcelona can beat Atlético Madrid when they face each other this weekend because Atlético Madrid is in amazing form, which could make it difficult for Barcelona to win against them.