Trying to predict the attacking formation that boss Arsene Wenger will start any match with is virtually impossible.

Who would have believed the Arsenal manager wouldn't start with Andrey Arshavin against Chelsea in their FA Cup semi-final showdown at Wembley? That was a decision which stunned and angered Gunners supporters.

Yet without Arshavin, who is cup-tied for tomorrow's clash, and the injured Robin van Persie, one can assume that Cesc Fabregas will be asked to supply the creativity needed to score an away goal at Old Trafford by continuing to play behind the main striker.

In fact, since his return from injury, Fabregas has played this role in every match apart from two - the FA Cup semi-final and the home leg of their Champions League quarter-final against Villarreal.

From his advanced role, he has created the majority of Arsenal's goals with his vision and execution of slide-rule passes.

Unusually for him, he has given the ball away or been caught in possession quite often but this is understandable because when playing further forward space is in shorter supply and his passes are aimed to unlock defences.

Although Emmanuel Adebayor looked uninspiring when entering the fray against Middlesbrough for the last 20 minutes on Sunday, his pace, strength and aerial ability must put him ahead of Nicklas Bendtner.

He also has an almost telepathic understanding with Fabregas. As soon as the Spaniard gets on the ball in central areas with a fraction of space, Adebayor will make a run between the opposition's centre-half and right-back.

That combination was evident when Fabregas created the chances for the Togo international to score goals against Manchester City and Villarreal.

Against United, that space will continually be available because their full-backs love to get forward as often as possible.

Theo Walcott is also becoming increasingly important to Arsenal's attacking play.

If United try to hold a high defensive line, press hard in midfield and deny the Gunners space to play, Walcott's pace will be key to breaking them down.

However, only Fabregas and maybe Frenchman Samir Nasri are capable of producing the necessary guile and cleverness to supply Walcott with a stream of passes and this is where Arshavin and Van Persie may be missed.

Walcott also allows Arsenal to counter-attack at pace, as seen when assisting Arshavin with his fourth goal at Anfield. While Patrice Evra will be fearful of his speed, he will look to expose Walcott's defensive lapses in concentration, just as he did at The Emirates Stadium in last season's 2-2 draw.

The left-hand side of midfield will probably be occupied by Nasri but Wenger may spring a surprise by starting Bendtner out there, just as he did to great effect against Roma in the home leg of their first knock-out round clash, leaving the Frenchman to play in central midfield.

While it is important that Arsenal pose a threat going forward, it is equally vital Wenger gets his defensive strategy right.

To stop United carving out chances, Arsenal must make their opponents' attacking play as predictable as possible, not allow them space in front of their centre-halves and be aware of the diagonal runs that the champions' wide players will attempt to make behind their defensive line.

To achieve this, Arsenal need to encourage United to pass into wide areas by condensing the space through the middle. Then when it does go wide, Arsenal have to work hard as a unit to keep the ball locked down that side of the pitch.

To ensure United's attackers are not allowed any space to drop into, Arsenal will play with two holding midfield players. Alex Song and Denilson will probably be Wenger's choices but their role in the Arsenal team is multi-functional.

They have to initiate Arsenal's passing movements, win the physical battles with their opposite numbers, support their full-backs when Cristiano Ronaldo is attacking them and continually be aware of the positional rotation between United's midfield and front players. Abou Diaby has all the attributes required to play the role but his understanding of the game and defensive decision-making sometimes let him down.

Wenger has also to decide whether he can trust the promising Kieran Gibbs at left-back. He was given a hard time by Dirk Kuyt's movement last week and Wenger will remember only too well that Arsenal's young full-backs, Justin Hoyte and Armand Traore, were destroyed by the movement of Ji-Sung Park and Nani in last year's humiliating 4-0 FA Cup defeat at Old Trafford.

If Wenger can get these key decisions right, Arsenal should take an advantage back to Emirates Stadium next week.