Actually I don't see Barcelona not taking their Champions League game seriously. Because of the results of their last two matches because a lot of players who are usually the first choice can't play because of the injuries they have. It is very difficult for them to qualify from this group stage because they have to finish 2 matches with a win, and also the result of the Inter Milan match will be very decisive for their next step in the Champions League. It would take a lot of magic to see Barcelona qualify for the knockout phase.
Barcelona really want to go as farthest as possible in Champions League because it means they will have more income to heal their finance crisis. I don't think it is a good explanation to blame all on injuries. Opponents of Barcelona did not have their best players for their matches too and all clubs must be able to cover injured players and achieve good results for their clubs.
Inter Milan and Bayern Munich are well deserved to go next in this group. Sorry but see Barcelona next season even it is bad to not have them in Champions League after next two match days.
The problem is that Xavi is too focused on their core players so indeed when some of their players get injured it becomes like a setback for Xavi.
Even though it seems like they are looking for excuses by saying Injuries to players, but whether they realize it or not, this has an impact on them. It's difficult when you look at their current condition, it's clear that there is a real difference when their main players play and when they are injured.
I think they are currently spending a lot of money, of course the expectations are high but with the current conditions they are gambling to return to losing money this season from a financial point of view.
If I understand you clearly, you are saying Xavi is not open to trying different players in the squad and prefers to stick to one set of players. When you look at the current Barcelona squad you will begin to wonder what the problem is if after signing up to 7 new and experienced players to the sauad and they still get bad results. The team us currently suffering poor performance and Xavi needs to do something about it.