Due to injury, Barcelona struggled in the Champions League last season. The team's leader, Xavi, had to solve this issue. The team won the title when the players improved and returned to La Liga. But the inconsistent defensive methods, such as employing Alonso as a left back, posed major problems.
Xavi must apply his domestic league teachings to the Champions League. In La Liga, Busquets and De Jong functioned well as a center, suggesting they may do the same in the Champions League. The summer transfer window brought in new players to strengthen the club and possibly aid Barcelona in the Champions League. With all these factors in mind, it's hard to determine when Barcelona will challenge for the crown. That appears to be in doubt.
Xavi has made major changes in Barcelona defense after they were eliminated from the Champions League last season, Barcelona has managed to become one of the teams that has a solid defense that is difficult for players from opposing teams to penetrate. This season, Barcelona defense has improved drastically, Barcelona's defenders have good quality and are very disciplined in guarding the defensive area.
Kounde, Araujo, Balde, Christensen, Alonso and several other players including Inigo Martinez will work together well to keep Barcelona defense area solid. Xavi will utilize quality players in his squad to maintain the form they showed in La Liga last season to go further in the UCL.
Concentration is needed in every match, and from what I saw last season they lost concentration several times which led to them being punished with a goal that they ended up losing. They usually have more of the ball, but in big games they seem to lose the creativity to break down the opposition's defense and that's why they struggle to score goals. In La Liga their performance was better, but I wonder why it was different in European competition, maybe it was the pressure or something else. Now they've made a move and that will hopefully be a positive thing in the future.