* Who stops Lionel Messi?

The 23-year-old World Player of the Year has turned in a slew of brilliant performances in Europe's elite club competition in recent years, destroying teams including Arsenal and Real Madrid with his pace and trickery.  United will have seen how Real Madrid have used centre back Pepe as an extra defensive midfielder in a largely successful attempt to negate Messi's impact but Alex Ferguson is unlikely to upset his well-established patterns to copy that approach. However, with his midfielders likely to be otherwise engaged, either Rio Ferdinand or Nemanja Vidic will have to step up to confront Messi in areas where the centre backs usually prefer not to venture.

* Chase all night or wait and strike?

Barcelona's midfield, marshalled by Spain playmaker Xavi, love to pass the ball and they are extraordinarily good at it.  In their semifinal first leg against Real Madrid at the Bernabeu, Barcelona had 72 percent of possession, an impressive feat in the lair of their arch enemy.  At times they appear to be toying with opponents. They pass and move brilliantly, and often instantly, but too often are allowed to do so unmolested. Park Ji-sung, in particular, will see it as his personal mission to be in the face of any Barcelona player who has the ball, harrying and rushing him so that eventually one of those passes will go astray. However, as others who have tried that approach before have found, it is exhausting work.

* Barcelona beware -- United can score too...

United have not progressed to their third Champions League final in four years by spending all their time worrying about the opposition -- they can play a bit too. They are at their best on the counter-attack, which is likely to be their approach on Saturday. Rooney's gradual development into a deeper-lying threat and his partnership with Javier Hernandez complete an attack that not many teams have been able to keep at bay for long.