Arsene Wenger has studied Manchester United at
their best and worst this season in order to plot the downfall of
the Champions League holders.

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 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."