Edinson Cavani limped off in Uruguay's World Cup round-of-16 victory over Portugal with an apparent calf injury on Saturday.
The Paris Saint-Germain striker was in visible pain near the 70-minute mark when he went down holding his calf, and moments later when Cristiano Ronaldo helped him walk off the field to receive treatment.
Once on the sideline, Cavani immediately asked to be subbed off. Cristhian Stuani took his place.
Cavani, who scored both of his country's goals in the 2-1 win over Portugal, admitted after the match he felt a pain in his calf and knew he couldn't continue.
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"I hope it is nothing and I can keep going," he said. "That is why I am saying that we will see how everything is.
"A study will be done and we'll see what can be done. I just felt this little pain and I couldn't go on."
Uruguay coach Oscar Tabarez, however, said it was too early to determine the specifics of Cavani's injury.
"He left injured, yes, and I don't know. I still haven't spoken with doctor," Tabarez said after the match. "The match just ended. We have played a lot of matches [and] he hasn't had a lot of rest.
"But we will take a look at him. We will do the necessary studies. But right now we can't say with any certainty what the injury is or might be."
When asked about the match's outcome, Cavani became emotional when speaking to reporters.
"I am very happy, truly content with what just happened," said Cavani. "I am so emotional right now. I don't have words to describe it. I am just happy, happy, happy and we have to keep dreaming.
"There is nothing better than to see the joy of the fans who are here. But I also imagine back in Uruguay, we have to keep going for them."