#3 Lack of squad depth
One of the major forces behind Real Madrid's consecutive European titles was their bench. The players like James Rodriguez, Raphael Varane and Alvaro Morata were up to ease the pressure off the main XI in the league matches week in and out.
Barcelona have issues when it comes to resting the first XI, the recent trip to Espanyol being the foremost case. The Catalans look nervous while playing with the likes of Andre Gomes, Paco Alcacer or Lucas Digne. Ousmane Dembele, the summer signing from Dortmund has recently been sidelined with injury. The best attacking options for the Catalans now come in the form of Paulinho or Alcarer.
The manager Ernesto Valverde cannot afford to take much risk with a major squad rotation. The league matches would be coming sandwiched between the crucial Champions League playoffs. The Cules would need some cautious approach with their star players as the fixture congestion increases.