Defender Yasuyuki Konno is a doubt for Japan's World Cup opener after suffering a knee injury.
The 27-year-old injured his right knee during the second half of Japan's final World Cup warm-up against Ivory Coast following a challenge by Arsenal's Emmanuel Eboue.
The FC Tokyo defender is set to be sidelined for two weeks, which would rule him out of the 14th June clash with Cameroon.
But he could be back when Japan face Holland on 19th June before rounding off their Group E campaign against Denmark five days later.
Japan coach Takeshi Okada said: "It is ligament damage so it's doubtful he will play in the first game.
"This kind of injury normally takes two weeks to heal."
Should Okada wish to replace Konno in his 23-man squad, the decision must be made 24 hours before Japan's opener against Cameroon in Johannesburg.
"There is still time so we'll have a look at him over the next two or three days. He was walking after the game and he is walking normally now," added Okada.
"The team doctor said it was touch and go whether he would be ready for the first game but I think it is probably best not to play him."