To progress to the last eight, the Azzurri need to win and hope Spain or Croatia are victorious or draw 0-0 in their match. A scoring draw in the Spain game would complicate the mathematics of a three-way head to head.
"There will be three or four changes," Prandelli told a news conference on Friday, the day after Italy let the lead slip in a 1-1 draw with Croatia.
"Obviously in the third game, with regards to who I pick, we need freshness. We have no margin for error."
Striker Mario Balotelli was substituted for a second straight game having failed to impress and Prandelli was unusually animated when discussing the inconsistent 21-year-old.
"I shouted at him for 15 minutes to play deeper," he said. "For me his potential is huge, but he has to do more. We are not a team that plays on the counter-attack. He had to be told the truth."
Antonio Di Natale could come in for Balotelli or fellow forward Antonio Cassano, who is struggling for full match fitness after five months out following heart surgery.
Prandelli said Di Natale was not totally suited to starting a game alongside another striker and suggested Alessandro Diamanti could play in the hole.
"Diamanti has the class to play as a second striker if the team is playing high up the park," added Prandelli who thought his side sat back too much to protect their 1-0 lead against Croatia and should have attacked more in the second half.
Italian media, well used to match-fixing and conspiracy theories, has gone into overdrive amid fears Spain and Croatia could agree to a 2-2 draw which would knock Italy out even if they beat Ireland.
An angry Prandelli rejected such talk.
"Spain will go on the field to win like they have always done in recent years," he said.
"After all their great football, the great spectacle, the fact everyone wants to copy their team, we think they'd think about conspiracies? Impossible."
