No one doubts Barcelona potential to get through the group phase as group winners, Barcelona quality is better than the other teams in their group. A number of Barcelona mainstay players injuries have had a big impact on their performance, Xavi had to use young players in several matches because his team was experiencing a player crisis due to being in the treatment room.
Barcelona is not yet fully able to compete with other clubs. The defeat that Barcelona just experienced in El Clasico indicates that Barcelona is still unable to maintain its momentum when it is ahead.
UCL which always presents big matches, will make it difficult for Barcelona when facing clubs such as Bayern Munich and Manchester City. There are still several tasks that Xavi must complete to make Barcelona able to compete with other favorite teams.
Barcelona is one of the teams that has managed to collect 9 points in the group, so it will be much easier for them to emerge as group winners because the opponents they face are much easier. Luckily, Barcelona is in a group with a team that is not too strong, so even though several of their mainstay players are injured, it doesn't really affect them in the Champions League. For competition in the Champions League, I think Barcelona will still be quite difficult because when the group stage ends they will definitely face a team that is much tougher and more balanced.
El Clasiko is a reference that when several of their mainstay players suffer injuries, it can affect the result of the match. Xavi Hernandez found it difficult to place players who had experience to stem the attack that Real Madrid players were trying to build because in a match like this, senior players who had experience were needed.