The two sides drew 0-0 at San Siro last week in the first leg but the former Spain international is anticipating goals in their return meeting at Camp Nou.
"I think Milan will score against us,” Guardiola admitted during his pre-game press conference in Catalunia.
“That's why we need to be very sharp on the attack and make the most of the chances we create."
||Barcelona are 20/1 with Bet365 to thrash AC Milan 5-0 in Tuesday's Champions League clash.
It emerged on Monday morning that influential Blaugrana midfielder Xavi was a major doubt for the visit of the Rossoneri because of a muscular problem but, according to Guardiola, the World Cup winner is in contention to start.
"He's been named to the squad; that means he could play," the 41-year-old coach stated.
Barca's second-leg showdown with Milan gets underway at 19.45 on Tuesday night.
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AC MILAN IN ACTION
|SPOLLI 57'||REFEREE: MAURO BERGONZI