It is everything Pep Guardiola did not want. Milan the opponents, no away goal in last week's first leg and Zlatan Ibrahimovic the jilted striker with a point to prove. While most of Europe takes it for granted that Barcelona will reach the semi-finals of the Champions League for the fifth consecutive season tonight there is another altogether less palatable scenario for the holders.
Hell hath no fury like a superstar centre-forward scorned and while Ibrahimovic has at least publicly calmed down almost two years since his departure from Camp Nou after just one season, tonight he is back for the first time, knowing his goals will count double and could dump the man he dubbed "the philosopher" out of Europe.
"When I walk into a room and Guardiola is there, he leaves. I don't know if he is scared of me," he said as he was sold to Milan two seasons ago. In his autobiography he also described the Barcelona dressing room as a cult and claimed the Barça coach was intimidated by Jose Mourinho. The words helped sell the book; now the world waits to see if the actions back them up. Ibrahimovic has a reputation for never quite living up to the hype.
He has been kicking around in the Champions League since 2002 but has never won it. He has twice left clubs only for them to win the tournament the following year. He moved to Barcelona to become a European champion, but while they won the tournament the season before he joined, and again the season after he left, while he was at the club it was Internazionale – the team he had left the previous summer – who were crowned champions.
He was underwhelming in the first leg last Wednesday. The Italian press complained that referee Jonas Eriksson had been Milan's most useful Swede, denying Barça two possible penalties. The famous Arrigo Sacchi quote that Zlatan is "strong against the weak and weak against the strong" still sticks.
He got 22 goals in 44 games during that solitary season at Barcelona but he had fallen out of favour by the time the season reached its climax. He failed to score in the last four weeks of the run-in as Barcelona won the league and he watched from the sidelines as they were beaten in the Champions League semi-final.
Tonight's mission will be made more difficult by the timely return to form of Gerard Pique, who will be charged with marking him. Pique and Javier Mascherano were so dominant against Milan that the home side failed to muster a single shot in the second half of the first leg and they paired up again in the weekend's home fixture against Athletic Bilbao, ensuring the visitors' first shot did not come until the 80th minute. In his last two appearances Pique has given away only one foul and won back possession 26 times. He is starting to live up to the "Piquenbauer" nickname once again.
"We've missed him," said Guardiola when asked about the renaissance. Now what is needed is for Cesc Fabregas to experience the same return to form. His signing was billed as bringing back together the class of 2000. But while Lionel Messi has ploughed on through the record books with another 54 goals this season, Pique suffered a dip in form and, after a flying start, Fabregas, the third of the reunited stars from that fabled under-13s side, has faded.
Fabregas watched gloomily from the bench as an unused substitute in the first leg. He then tweaked a muscle in his back in training the following day and was left in the stand for the weekend's league game against Bilbao. Barcelona originally claimed his absence had been a "technical decision" but Guardiola said after the match on Saturday: "He couldn't move his back. We had to give him an injection and he improved but not completely. We did not want to force him ahead of the biggest game of the year."
Fabregas trained normally yesterday and should start tonight. He is Barcelona's second top scorer with 15 goals this season but he has not hit the back of the net for almost three months. The 3-4-3 system used frequently in the first half of the season left him at the top of a midfield diamond just behind Messi.
The two clicked as if Fabregas's Arsenal adventure had never separated them but as Guardiola reverted to a back four he has at times been forced to play wide in a front three and has struggled. "I need to learn the movements and keep up with the coach's upgrades," Fabregas says. "I grew up in this club but it is still not always easy." He was Arsenal's hero against Milan in 2008 when, after a goalless draw in London in the last 16, he led the team, scoring the first in a famous 2-0 win at San Siro.
Xavi Hernandez did not train yesterday and with a recurring calf injury remains a doubt. His absence would mean even more resting on the former Arsenal captain's shoulders.
Guardiola's team has never fallen at the quarter-final stage of a knockout competition. But a repeat of Milan's first-leg resistance will test that record. More heroic throwing themselves in front of goal-bound shots from the likes of Massimo Ambrosini and Luca Antonini and all Milan will need is for someone to stand up and be counted at the other end of the pitch – an Ibrahimovic, a jet-heeled Kevin-Prince Boateng, rested at the weekend, the former Real Madrid forward Robinho or even a fit again Alexandre Pato who will start on the bench.
Barça remain favourites but there is a sense that they could have done to them what they did to Chelsea in 2009. After a 0-0 at Camp Nou Guus Hiddink's side took the lead through Michael Essien but with almost the last kick of the game Barça equalised through Andres Iniesta and went through on away goals.
At the weekend Iniesta extended an incredible run of 52 league games without having been on the losing side for Barcelona. This team are not used to defeats. But not losing will not be enough tonight.
This is game number 50 in the Champions League as a coach for Guardiola. All things being equal it ought to end with him celebrating reaching his fourth semi-final in four years. But right there is Barcelona's potential problem. All things are not equal.
Allegri's immediate reaction to the first leg 0-0 was: "There are three possible outcomes now, and two of them suit Milan." Away goals count double and if he scores one himself, no doubt Ibrahimovic will be the first to tell us that his has counted for a whole lot more.
Barring Barça's path: Three who could inspire a shock in the Nou Camp
Zlatan Ibrahimovic: The Swedish striker will be eager to prove himself against his former club
Massimo Ambrosini: Showed in the first leg he can contain Lionel Messi
Luca Antonini: Will take confidence from his heroic display at full-back in Milan
Five reasons why Milan can beat Barcelona
1 They know what it feels like to get a score draw at Camp Nou, and they did it this season. Despite the fact that Barça dominated the group game, with 17 shots and 11 corners, it ended 2-2. That result would see the Italians go through tonight.
2 Alexandre Pato scored Milan's opener in that 2-2 draw and he is fit again after a month's lay-off, having had treatment in the US for niggling leg muscle problems, from the specialist Frederick Carrick. If Robinho fails to deliver as he did in the first leg, Pato will give Massimiliano Allegri options from the bench.
3Lionel Messi (right) may be one goal from becoming the first player to score 13 times in one Champions League season and two away from matching the all-time European Cup record, held by Milan's Jose Atalfini (1962-63), but Barça's all-time top scorer has a poor record against Italian teams. Messi has played seven Champions League games against them and he has scored just one goal – though it was against Milan at San Siro, it was from the spot. Milan are also the only side in the last 10 games to have prevented him scoring.
4Zlatan Ibrahimovic has a point to prove and this is the place to do it. The Swede cost almost €70m (£58m) in 2009 but the most expensive player in Barça's history was never going to be more important than his strike partner, who cost nothing. Tonight the Swede can finally get the better of Messi.
5Milan have never gone out of the European Cup after drawing 0-0 at home in the first leg. Three times they have shut the opposition out at home without scoring themselves and three times they have progressed. They also play the holders knowing no side has been able to retain the European Cup in its present format.