Uruguay head coach Oscar Tabarez said on Saturday that he was worried because of forward Edinson Cavani’s injury, as there was a little time for recovery before the next game.
Cavani scored a brace in his team's 2-1 win over Portugal in the World Cup round of 16 match on Sunday (AEST), but sustained an injury and was replaced in the second half of the game.
Uruguay have advanced to the quarter-finals, while Portugal have been eliminated.
“He felt pain," Tabarez said of Cavani.
"We have not yet spoken to the medics, the game has just finished. There is a little time for recovery, we will consider [the situation] after a day of rest. Of course, we are worried, but it is not yet clear how serious his injury is."
Uruguay will face France, who beat Argentina 4-3 on Sunday (AEST) in Kazan, in the quarter-finals on Saturday (12am AEST).