Italy captain Paolo Maldini could miss the group G game against Croatia on Saturday after twisting an ankle in training.
Maldini limped off towards the end of Italy's training session and team doctor Andrea Ferretti said he would take another look at the injury on Saturday.
"He twisted his left ankle. There is no swelling but there is some pain. We will see tomorrow, we need to wait 12 hours. There is certainly a chance (of Maldini playing), it is a just a question of the pain," said Ferretti.
Maldini said he was optimistic of his chances of being fit. "I hope so, I believe so. It is not too bad we will see tomorrow if it swells up or not. I hope to make it because it is an important game for us," said the Italy captain.
Coach Giovanni Trapattoni was also upbeat about Maldini's chances.
"I think it is nothing serious. The player is also optimistic himself and the doctor is quite optimistic. We will have to weigh it up tomorrow but of course I have to think of solutions for a team without Maldini," he said.
Maldini would miss a chance to beat Lothar Matthaeus's record of 25 appearances in the finals if he does not face Croatia.
More importantly for Italy, Maldini's absence would cause a selection quandary for Trapattoni who had seemed to be settled on his side.
The Italy coach has been transparent about his intentions so far in the World Cup but in the immediate aftermath of Maldini's injury he declined to name a replacement should his captain miss out.
"It could be a defender or it could be a midfielder," said Trapattoni, who also suggested that the versatile Christian Panucci, who played at right-back in the 2-0 win over Ecuador on Monday but was expected to move into midfield for Saturday's game, could play on the left of a three-man defence.
"I could move Panucci across there and I could also change the tactical formation," he added.
Pressed on his likely side the Italy coach replied: "There will be eleven players".
Goalkeeper Gianluigi Buffon said Maldini, Italy's most capped player with 123 appearances for his country, would be missed not only for his skills in defence but for his personal qualities.
"It is important because beyond being a defender and captain he is very charismatic. But we have a lot of players in our squad," added Buffon.
Croatia lost their opening game in the group 1-0 to Mexico.