The decline in Barcelona's performance cannot be separated from the fact that many of their main players are injured and this team does not have substitute players who have equal quality to maintain the team's performance so that it can become like now, this is quite unfortunate because this makes Barcelona even further behind.
I agree that the decrease of Barcelona performance is caused by too many injured players. Some of them are the key players like Lewandowski, Kounde, Pedri, Frank de Jong, and Raphinha. However, some of them have recovered now, Lewandowski and Raphinha have played yesterday. But they need time to be back to their best shape. It is not easy to play again with their best after they spend much time for the recovery.
I think, losing Dembele and Ansu Fati also contributes to the decrease of Barcelona performance. I still remember that these players often give the difference when they played in big matches in the previous season. I am a bit confused why Xavi doesn't need them anymore. Xavi may not know that losing them will bring a big impact.