Barcelona cannot challenge or rival Real Madrid for the La Liga title next season because they don't have a good squad that can perform better than Real Madrid's squad. Barcelona is still in the rebuilding stage, so I don't expect them to win the La Liga title next season. Barcelona's target next season should be to finish in the top four of the La Liga table so that they can qualify for the UEFA Champions League competition. If Barcelona's new coach can build up Barcelona's squad in this transfer window and the next transfer window, maybe they will start challenging Real Madrid for the La Liga title.
Barcelona can rival Madrid but not in this season, they may not succeed at it this season of they attempt it, Barcelona have a relatively weak squad when compared to that of Madrid and that isn't in doubt but if you are to make comparison with other weak or smaller teams in la Liga, I believe Barcelona will not be really doing terribly because they have some fairly good players in the squad who if they are properly utilized, they are going to produce results well enough for the team. Madrid has got a very tough team which none in the la Liga can really contend firmly.
I believe with the new coach Barcelona have gotten they will start again to build on their strength and if he's very strategic enough, he's going to be able to see how well he will grow the strength of the team over a few period of time even if it's not in the immediate season but within two seasons, if he's give such luxury of time, the team should have improved far beyond what they are now a d become very strong and firm contenders in the la Liga such that almost every other team will not be able to just contend them and win easily except they too just like Madrid becomes tough enough.