Barcelona head coach Gerardo Martino rubbished reports Milan are in "crisis" and believes the two sides are well matched.
Massimiliano Allegri's side have endured a torrid start to the Serie A campaign, taking just 12 points from 11 fixtures, to occupy 11th position.
By contrast Barcelona have stormed to the top of La Liga, taking 34 from a possible 36 points.
The two sides played out a 1-1 draw in their UEFA Champions League fixture at San Siro on October 23, meaning Barcelona can qualify for the round of 16 with a win in Wednesday's return fixture.
But Martino is adamant Milan pose a huge threat ahead of the showdown at Camp Nou, and warned his side not to take their Group H opponents lightly.
"Tomorrow we must play the way we know how, move well and not allow Milan to close up too much in defence," he said.
"That system is difficult to overcome.
"I don't believe there is any difference in the way Milan come into this match or Barcelona's form. We are on level terms.
"I always feel suspicious when people say big clubs are in crisis. Milan have a great history and great players. They might not be in a great moment, but we must always respect them.
"It is of vital importance to win so that we almost certainly qualify with two rounds to spare. I think we can improve, both as a collective and individually."
Martino was also pressed on Lionel Messi, with the Argentina international netting just one goal in his last four matches since recovering from a thigh injury.
But the 50-year-old remains unconcerned by Messi's barren run.
He added: "We are all very relaxed about the situation. He might not be 100 per cent, but he is training well.
"We introduced a group of strikers who are able to play throughballs, but also maintain possession."
|10||L. Messi||30' 83'|
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