The Gunners head to Old Trafford for Wednesday night's semi-final first leg having rediscovered some consistency which pushed them back into the top four of the Barclays Premier League.

However, Wenger's plans have been hit by injuries, first to the regular backline - although goalkeeper Manuel Almunia is expected to be fit to face United - and now leading scorer Robin van Persie is sidelined by a niggling groin problem.

Nevertheless, Arsenal, who cannot field the ineligible Russian playmaker Andrey Arshavin in Europe, still have the personnel to cause any side problems - as Villarreal found out to their cost in the last round.

Captain Cesc Fabregas has been deployed in a more advanced role for the Champions League games, giving support to marauding wingers Theo Walcott and Samir Nasri, while backed up by midfielder enforcers Denilson and Alex Song.

Wenger, however, knows his tactics must be spot on if they are to "annihilate" the potent attacking threat an in-form United side can be.

"We do not necessarily change our formation depending on who we are playing that day. We simply try to find the best way to express our own qualities, while also trying to annihilate the strong points of the other team," Wenger said in the May edition of the official Arsenal magazine.

"So it is a compromise. We look for a shape where we can express our strong points, as well as stopping theirs.

"When we scout the opposition we watch tapes of them losing and winning.

"We watch them scoring and conceding goals, so we try to exploit the weaknesses they have, which every team has."

Wenger, though, maintains: "Nothing is permanent.

"We always look for the best solution.

"No formation can ever solve all the problems, but you always try to find the system which suits your players the best and that gets the best out of your qualities.

"So I would never say that it is for definite that we will also use this system."

Wenger knows possession, and making the most of it, will be key to Arsenal's chances of taking an advantage back to Emirates.

"The technical level is so high in the Champions League, so it is important not to lose the battle in midfield. You have to be defensively sound as well," said Wenger, whose side beat United in the Premier League at Emirates earlier this season through a brace from Nasri.

"Most of the time in recent years we have played this formation in Europe because you need to have a good engine and not be outnumbered in the park.

"The best players in the world play in England now, so that is why the quality is so high."

Given the loss of William Gallas to a knee injury for the remainder of the campaign, veteran defender Mikael Silvestre has found himself handed a run in the side.

The 31-year-old Frenchman, signed by Wenger in the summer, was part of the United squad which lifted the European Cup following a penalty shoot-out win over Chelsea in Moscow last May.

After spending some nine seasons at Old Trafford, Silvestre is relishing the chance to go up against his old club.

"I still have got a lot of friends (at United), but it is part of the competition," said Silvestre.

"You go to a match and you want to fight, no matter you play against, even if it is your best friend in front of you.

"When you have to tackle, to win the ball, when you have to play the challenges, you fight for your club and you forget everything else."