Barça-Man Utd: Key battles

Barcelona are going with Abidal despite a disappointing season after signing from Lyon because of his greater defensive capabilties compared with Sylvinho. The Frenchman will have to be more than wary of the player many regard as the best in the world. Make no mistake, this is Ronaldo's biggest stage yet: he will go down in history if he turns it on for a United win tonight.

The importance of Argentine whiz-kid Messi to Barcelona's cause cannot be understated. And it is not enough this season to 'do a Liverpool' - the team that knocked them out last season - and stick the full-back to him like glue, especially at the Camp Nou. Patrice Evra must do what he can at left-back as the left-footed right-sided player skips inside and across the pitch; then it is up to Rio Ferdinand and Wes Brown to block his entry-route to the penalty area and goal.

Livewire front man Eto'o will be as bouncy as an over-sugared child on a bouncy castle and have to be kept in check as his team go on the attack. Nemanja Vidic is out, replaced by the less secure Wes Brown, meaning the main responsibility will fall to Ferdinand. The centre-half must perform to the standards set over a league season in games such as this and then some if United are going to win the Champions League again any time soon.

Barça captain Carles Puyol is suspended for the first leg and his brand of boundless energy and commitment will be sorely missed. Stand-in centre-back and Mexico captain Marquez has been criticised recently for his attitude and the spotlight will fall upon him as United's star striker Rooney looks to silence the Catalan hordes with a typical sparkling display up front.

Silent assassin Scholesy will prowl on the counter and look to get on the end of moves from Ryan Giggs on the left and Ronaldo on the right. He will be tracked by Barça's main defensive midfielder and Ivory Coast international Toure, who will have a job on his hands.