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Losing to Arsenal was not supposed to happen, not after adding some crucial players to the team this summer. Furthermore, there are certain good numbers of targets ought to be reached this season. Xavi Hernandez will restrategize and implement new game structure, because the blaugrana becomes very weak towards elite clubs outside their league. Barca always dominate games within La Liga but are not giving the same energy in other top competitions, that's their weakness, comparable to PSG in Ligue One. Their ultimate target is the UCL title, I doubt if they will make it to the knockout stages this time.
Losing important defenders who have a lot of experience, I mean Sergio Busquets and Jordi Alba, probably had a big impact on Xavi. Although statistically Barcelona possession of the ball is better than Arsenal, but their defense is not as strong as when these two senior players are in this team. Xavi doesn't have to restrategize only but he has to improve his team mentality as well, especially the Barcelona defenders.