Manchester City forward Sergio Aguero was hospitalised at half-time of Argentina's clash with Nigeria.
The 29-year-old fainted in the dressing rooms at the interval and was quickly taken to hospital.
The Argentine Football Association said on its Twitter account that Aguero "had a blackout and was taken (to hospital) so routine examinations were made only as a precaution."
Referencing previous heart problems, Argentinian team doctor Donato Villani told reporters: "He felt bad twice, and with the medical history he has, since he was operated on when he was 15, we wanted to be sure it was nothing.
"We took him to hospital to make sure everything was normal, we prefer to wait to be sure."