Uruguay manager Oscar Tabarez expressed his concern over Edinson Cavani's condition after the forward set up a World Cup quarter-final date with France.
Cavani's double accounted for Portugal as Uruguay won their last-16 clash in Sochi 2-1 on Saturday night.
But the Paris St Germain striker was forced off in the final quarter with a leg injury and could now miss Friday's quarter-final against France, who reached the last eight earlier in the day by beating Argentina 4-3.
Cristiano Ronaldo helped Edinson Cavani off the pitch in the final quarter of Saturday's game
'He was injured and he felt pain,' Tabraez said in his post-match press conference.
'I don't know right now exactly because I have not spoken to the medical team.
'But in five days we have a match and we don't have a lot of time for recovery here.
'We will have an analysis and a diagnosis in time, but right now we are only worried of course. 'We don't know for sure how grave this injury really is.'
Uruguay had to withstand fierce late Portugal pressure as the European champions chased an equaliser.
Cavani was forced off the pitch after sustaining a leg injury in the win over