He believes Japan's Italian coach Alberto Zaccheroni's familiarity with his compatriots might cause Italy problems.
"Japan will have the slight edge, I think, because they have an extra day of rest," said Prandelli.
"Plus, Alberto knows us very well, he knows how we work. I expect him to prepare a trap for us.
"From tonight, we will begin planning for the Japan game. I trust that he will come up with an interesting strategy against us," Prandelli was quoted as saying on www.fifa.com.
Italy have never lost to Japan but goalkeeper Gianluigi Buffon knows they must improve to stand any chance of winning the Confederations Cup for the first time.
Italy opened their account on Sunday with a 2-1 win over Mexico at the Maracana Stadium in Rio and face the Japanese in their second match in Recife on Wednesday.
"Success is being crowned champions and that is our objective," Buffon was quoted as saying by Globo on Monday. "You do that by paying attention to the details. We'll certainly be better against Japan than we were in Sunday's game."
Japan need to get points on the board after losing 3-0 to hosts Brazil in their opening game on Saturday.
"We take the field knowing that this is like a final for us," said Zaccheroni. "We will be giving it our all, because we know that if we lose it's all over."
