After a shocking home defeat against Hercules on Saturday, Barcelona are expected to bounce back and beat Panathinaikos with a convincing performance.
Against the Greek, Barcelona cannot afford another slip-up. Panathinaikos have a very good team, with players like Djibril Cissé, Sidney Gouvou, and Gilberto Silva, and they should be a formidable opponent.
However, Barcelona will certainly be looking to prove that they're still the best team in Europe, and must be considered favorites for this match.
With Puyol finally back, Guardiola is likely to field a full-strength squad: Valdés, Abidal, Puyol, Piqué, Daniel Alves, Busquets (Mascherano hasn't fully adapted yet), Xavi, Iniesta, Pedro, Messi and Villa.
Xavi's performance will be crucial.
Against Hercules, it was shown once again that Barcelona are just not the same team without Xavi, who didn't start the match. In the middle of last week, Spain lost 4-1 to Argentina. With Cesc Fabregas on Xavi's spot, Spain were unable to take advantage of the tiki-taka style. There is only one Xavi, and currently no one can replace him.
Xavi is widely regarded as the best midfielder in the world, and despite Lionel Messi's fame, he is the most important player on this Barcelona team. Make no mistake: If Barcelona want to win everything again, they will need Xavi to play at his usual level for the whole season.
Against Panathinaikos, the Blaugrana fans expect to see Xavi controlling the midfield and leading Barcelona to victory. They also expect to see Messi and David Villa score again, after disappointing performances from both against Hercules.
Only a team with the same attitude and hunger as in the past two seasons can bounce back and beat Panathinaikos in an emphatic way.
A convincing win here will help Barcelona get their confidence levels back. Another disappointing performance could mean trouble for Guardiola's team, especially because their following match is against a very strong Atletico Madrid side.
These two matches might start determining Barcelona's fate this season. Will Xavi, Messi & Cia. rise to the occasion like they always have in the past?