Allegri was able to name Pato, Alessandro Nesta and Christian Abbiati in his matchday squad, so provided an update on the trio.
"I saw Pato yesterday after a month. He took part in his first training session and he'll take part in the second tonight. I'll evaluate things after that. You don't need to be that fit to play 30 minutes.
"As far as I know, Abbiati has no problems. I'll see about Nesta after he trains at the Camp Nou tonight.
"From a tactical point of view, given that we play every three days, I haven't had the time to prepare for it properly.
"We'll do that tonight even if we already know them well given that we played against them only last week."