The talented 20-year-old has been struggling with injury, and although he has travelled with the squad to take on the Premier League champions, Galliani is not confident that he will be ready in time.
“It’s unlikely that Pato will make it and I think [Marco] Borriello, [Klaas-Jan] Huntelaar and Ronaldinho will play up front,” he told Sky Sport 24.
Leonardo's side trail 3-2 from the first leg after Ronaldinho's early opener was cancelled out by Paul Scholes' strike and two headed goals from Wayne Rooney.
Clarence Seedorf's late back-flicked effort has given the San Siro side a glimmer of hope of reaching the last eight.
And although the Italian giants will need to score at least twice at Old Trafford to progress, Galliani has not yet given up hope of an upset.
“We can do it, this is the feeling I get after that first leg,” he said.
“We think we can put up a fight, but I won’t make predictions. It is an exciting game, like many that we have faced throughout this club’s history.”
NEWS: Maldini - Milan must forget first leg loss
