Oscar Cardozo is a fitness concern for Paraguay just four days before their opening group game with Italy.
Cardozo earned the call to the national squad following his impressive season with Benfica in which he scored 36 goals.
However, he may miss out in the opening match as worries mount that he has not fully recovered from a niggling ankle injury.
Cardozo has been battling with the same issue since April which is now threatening his early participation in the tournament.
"Cardozo's injury is more serious than we thought and we are worried," said Paraguay's technical director Horacio Cartes.
The 27-year-old, who has been training separately from the team, will face a race against time to be fit for the group opener.