#3 Overdependence on Lionel Messi and Luis Suarez
In the absence of Neymar Jr and with Andreas Iniesta out of form, Messi has to do the dual job of creating the goals and scoring them. Whenever they play Barca, Atletico's first tactic is to close down Messi and if no one man can do it, they accomplish it collectively.
Atletico Madrid will throw men into his path and will deny him the freedom to dribble and shoot. Simeone's men usually close down Messi as soon as he gets the ball and never give him any time or space to play freely.
Atletico players crowd centrally when Barca attack from the middle of the pitch, thereby cutting any kind of supply to Suarez. Suarez will have to track back from the box to link up with Messi and therefore, Barca will be reduced to having very few bodies in the 6-yard box.