The pre-match hype to this week's Champions League match at the Camp Nou has so far focused on Barcelona's defensive conundrum and the availability of Lionel Messi, yet neither issue holds the key to this tie.
The Catalans are justifiably popular favourites to win this season's title, but their triumph hinges on necessary improvements following last week's efforts against Paris Saint-Germain.
Blaise Matuidi's deflected equaliser in injury time ensured Barca left the Parc des Princes with a bittersweet taste in its mouth.
"Bad luck" somewhat contributed to the underwhelming result, but it is said in football you create your own luck.
Tito Vilanova's men controlled the game for much of the night but lacked the tempo and intensity which allowed them to steamroll Massimo Allegri's AC Milan.
The Parisians might be down on away goals, but expect few changes from Carlo Ancelotti.
PSG do not need to go looking for their goal. Their chances will come—that much is guaranteed against Barca.
If the Blaugrana make the following improvements to their game, however, they will move one round closer to a final in Wembley.