Xavi Hernandez would encourage his new young players to suit up for the main squad, because it's time to elevate the team to the next level, no longer counting on the primary players, but rather sticking to future plans, which are the young players who are eager to start for the team, which might crumble currently, but they will definitely become stronger in games. I doubt Barcelona will reach a vital stage in the UEFA Champions League this season because they are woefully underperforming in La Liga but are yet to show any signs in UCL competition.
In the Champions League Barcelona has quite the advantage over the teams that are not that strong in group H, but in La Liga Barcelona is still able to be beaten by its true rivals like yesterday at home so it is appropriate for Barcelona to use young players in their squad without more reliance on aging main players. I also think that in the Champions League this season Barcelona will not run smoothly because there are many strong teams that will be obstacles for him, but in La Liga Barcelona still has the opportunity to make improvements in order to advance to first place this season.