The Rossoneri host the Blaugrana at San Siro on Wednesday, and the 68-year-old is well aware of the threat the opposition midfield, along with the Argentine, will pose.
"It will be a great event, a great game. It is beautiful to be in a position to be a part of this game," he told reporters.
"We’ll be up against the best side in the world. Look at their midfield - it’s the one with which Spain won the World Cup and European Championship.
"[Plus], Messi is the best player of all time. He is even better than Diego Maradona and Pele."
Galliani went on to acknowledge that the Catalans are heavy favourites going into the tie, but stressed that his side are intent on causing an upset.
"I won’t make any prediction as I can’t see into the future, but we believe," he added.
"Barca are favourites, but the favourites don’t always win."