The Azzurri won through to the last four with a hard-fought 2-1 win over Belgium in the quarter-finals after goals from Nicolo Barella and Lorenzo Insigne.
Italy are the only side with a perfect record during this Euros, but that hasn’t stopped some criticism directed at Lazio striker Immobile.
Immobile, who was on the ground injured as Barella scored the opener against Belgium, has managed two goals at Euro 2020.
“He is the Golden Boot, one of the best scorers of the last few years,” Mancini said.
“Sometimes the most criticised are the decisive ones during the Euros or the World Cup.”
Mancini was also wary of Spain, who he said offered a different threat to his past opponents Belgium and Austria.
“It will be difficult, even if Spain is different from Belgium. It wont be a match like that, but with many difficulties,” he said.
“With Austria it was difficult because it was the first knockout game but also because of their aggressiveness.
“Tomorrow it will be the same but it will be difficult, Spain has been extraordinary for years even if now there has been a change and they are younger.
“They have a good coach and very good players. In the last twenty years they have dominated football in the world, they wont change now.”
Immobile is the bookies’ favourite to be the first goal scorer, marginally ahead of Spain’s Alvaro Morata.