Atletico is likely to start Lucas, the 20-year-old CB, again with Godin. Lucas performed well in the first leg, but he's not the same threat to score a goal as Savic or Gimenez, both of whom are injured. In a game when a goal is huge for Atletico, it's hard to lose a scoring option.
What is the point of your post? I don´t know Atletico´s squad well enough to make a judgment, but if they don´t have any other players available to injury (or in F.Torres´case due to suspension), you have to pick others and not look back or argument "could-would-should have"...A defender has to defend first, especially against Barca in this leg with this previous result. You cannot look for a defender who may be great for offensive set pieces, but a weakness (to exaggerate) in defending in general, IMO.
I think Atletico played a good defensive game in the 1st leg as long as Torres was on the field (they also did a good defending with 10 men, but with him on the field it should have been better), so the thinking should be,
"we play our defensive game, bring in a new forward and try to score a goal while holding up on defense". This is incredibly hard, but what can you do? Atletico cannot come out and play a possession-dominating game against Barca and hope to outscore them 3-1 just because they have three attacking midfielders in central midfield. 90 minutes can be very long and they need only one goal - although it will be incredibly hard to keep Barca from scoring, we just saw the same happening in their last league match with Real Sociedad.
If Atletico scores first, it´s another game, Barca has to attack and there should be more chances for counter-attacking for Atletico, maybe even a 2nd goal is in play.
If Barca scores first, Atletico needs two goals, which will be incredibly tough to overcome. So you should stay away from Barca leading and just wait, as Atletico.