I'm not going to write a full tactical preview for Barcelona vs. Chelsea, because they haven't changed much in the last week or so (apart from losing twice). If you want some tactics reading, the preview of the first leg is still fairly relevant. However, there's at least one interesting tactical problem that's going to pop up tomorrow at the Camp Nou - the presumed return of Gerard Pique to Pep Guardiola's starting lineup.
The wonderful Jonathan Wilson highlighted the importance of the centre back to the Catalans' chances of advancing in his tactical preview of the match:
[Pique] remains supreme when it comes to covering [Dani Alves'] surges. He would also give Barca a second six-footer (with Sergio Busquets). It's not much, but two is still better than one and it might do something to alleviate Barca's clear problem with set-plays and high balls.
Obviously, Pique would also make it more difficult for Didier Drogba to dominate Barcelona's centre backs as easily as he did last week. Javier Mascherano is a far softer target than the 6'4" Pique, and Drogba is unlikely to have as large an impact as he did in the first leg should Pique play, in addition to the 25-year-old shoring up Barca's play on set pieces and improved covering for Alves as well as his strong distribution.
That said, there's a reason that Guardiola hasn't included Pique for five games running, and that's because for all of his gifts he hasn't really been very good this season. Pique has been prone to errors both on and off the ball (think a less sexy David Luiz and you won't go far wrong). Including him has obvious benefits, but a Pique-Mascherano pairing also represents a significant gamble.
Playing those two would presumably have knock-on effects elsewhere, most importantly at left back. If Pique plays, we might see Carles Puyol at left back rather than Adriano, which would make the inclusion of Juan Mata in Chelsea's lineup more tactically sound. The playmaker was deployed as a right winger by Roberto di Matteo in the first leg, and he was easily the least effective player on the pitch, allowing Adriano to go by him at will and touching the ball basically never.
If Puyol, who's a far more conservative fullback, plays instead of Adriano, Mata would have less defensive responsibility on the right and could therefore be a little more aggressive in moving Chelsea up the pitch. Of course, since Barcelona need at least two goals at the Camp Nou to avoid extra time, they might just go for broke and pile everyone forward, at which point Mata will have some defending to do anyway.
Regardless, if Pique plays, that changes the way Chelsea will have to do things tomorrow. Hopefully we can cope with it.