"I only know three or four Japanese players and the most talked about is the one that plays for Manchester United, Kagawa, he is the star," De Rossi told reporters on Tuesday.
"I think they are well organised and I think that means they will be dangerous."
The Italians made a winning start on Sunday when goals from Andrea Pirlo and Mario Balotelli secured a 2-1 win over Mexico in Rio de Janeiro.
Italy coach Cesare Prandelli got a laugh when he discussed how to handle the mercurial former Manchester City forward but said Balotelli's good form was down to his own hard work.
"Talking about Mario is difficult because you never know what he might do from one day to the next," Prandelli said.
"I think he is strongly motivated by wearing the Azzurri shirt and he has found a group of players here who have won a lot and want to win a lot more.
"That helps him grow. We have said for years that he has great potential and our task is to let him fulfill that and we need to contribute to that and help him as well."
Prandelli said Wednesday's game could depend on how his countryman Alberto Zaccheroni sets out the Japanese.
"They have a great coach who can use the players' qualities to the best of their abilities," Prandelli said of the man who took over in Japan three years ago.
"He is also very good at putting out balanced teams. They are good players with good concentration and commitment and it is a very interesting team."
He warned that losing three goals in the last two games - two against Haiti - could lead him to put out a more defensive formation against Japan.
"Clearly every team has to try and improve and we need to be more practical in attack," Prandelli said. "The very final stage, we need to improve that."
Wednesday's game is only the third meeting between the teams, with Italy winning one and the other drawn. Zaccheroni will become the fifth coach to face his home nation in the Confederations Cup.
