Viviano is shining on-loan with Palermo this season.
"Emiliano can become a great if that is what he wants," Galli told Il Giornale di Sicilia.
"It would be a shame if he doesn't take advantage of the qualities that he has and I often tell him that," he added.
"He has the misfortune of having a great goalkeeper like Buffon ahead of him in the national side. It happened to me too with Dino Zoff, but I'm certain that Viviano is the best second choice."