That can be the case at the Emirates in an important game for United and Arsenal, a tricky team because they have a combination of players in attacking positions who have great movement and are hard to mark. They have similar players across the field in attacking areas and they're not confined to one role, so it's a very fluid system with only Olivier Giroud – playing as a traditional no.9 – with more of a fixed position. He's not unpredictable in that sense, but Arsenal's other forwards are always on the move and someone like Jack Wilshere can bring it all together and is unafraid to take the ball in any situation. Defensively, United have to be alert to that mobility in the Arsenal attack.
Arsenal have quality players and a big defeat like they suffered against Liverpool is a kick in the back of the head. That result makes them more dangerous because it's a wake-up call. They were very poor in the first half, going in 4-0 down at half-time. But in the second half they got the ball a bit more and controlled the tempo. It still wasn't good enough but they will be aware of their mistakes and will be determined to make sure they don't do the same things again against a United team who need points and a big result.
Of course, there's always focus on van Persie in this fixture. Players often do well against their old clubs and Robin has three goals in three games against Arsenal. As a player you have a stronger motivation against your old team and an awareness of what their weaknesses might be. Robin didn't celebrate his first goal against them, and that's out of respect, but since then he has looked pretty happy about scoring past them. Hopefully he keeps that run going on Wednesday.
Louis Saha was speaking to ManUtd.com and also appeared as a guest on MUTV's Matchday Live show for the game against Fulham.