As the teams and hordes of fans arrive in Rome for the 67,000 sellout, Barca coach Josep Guardiola [ Images ] has much to ponder.
The Spanish champions will be without three of their first choice backline for the clash at the Stadio Olimpico (7:45 p.m. British time), with fullbacks Daniel Alves [ Images ] and Eric Abidal [ Images ] suspended while central defender Rafael Marquez [ Images ] misses out through injury.
Guardiola, in his first year in charge, may opt to shift midfielder Seydou Keita [ Images ] to left back ahead of Silvinho, with Yaya Toure [ Images ] continuing to fill in at centre back and captain Carles Puyol [ Images ] possibly shifting to the right.
For holders United, centre back Rio Ferdinand [ Images ] sat out Sunday's 1-0 win at Hull City along with the rest of the Premier League champions' first team and coach Alex Ferguson [ Images ] is hopeful he will shake off a calf problem.
"Rio is coming along fine. I think he is on course to play Wednesday," coach Alex Ferguson told MUTV.
However, United midfielder Michael Carrick [ Images ] is aware last season's semi-final between the pair was far from pretty, with the English side prevailing 1-0 in the second leg at Old Trafford.
"We thought it would be very open and attacking when we played them last season and in the end there was only one goal over two legs," Carrick told www.manutd.com.
"They can score and create chances at any time but we believe we can defend well and attack them."
Carrick's comments suggest United may be prepared for another 'smash-and-grab' raid, where they nullify Barca's attacks and hit them on the counterattack.
The plan worked to perfection in the semi-final demolition of Arsenal [ Images ], where world player of the year Ronaldo scored one of the goals of the season in a quick break from United's own box.
The Catalans say they are not interested in United's tactics and want to show off their full array of talent, which failed to shine in their fortunate semi-final victory over Chelsea [ Images ].
"Since I don't know what sort of game they'll play, what we have to do is get hold of the ball, dominate midfield and attack," midfielder Xavi [ Images ] told a news conference before jetting into Italy's [ Images ] capital.
"Winning means we have to impose our own style. The boss has told us to play the way we have all season, to enjoy ourselves and go for it from the off. He also reminded us that we need to control our nerves and emotions."
Rome police will begin a huge security operation later with a partial alcohol ban in force in some areas of the city. Trouble has marred United visits to play AS Roma in recent years.