Argentina team doctor Daniel Martinez said on Thursday that Aguero is receiving treatment and will be evaluated ''day by day.''
Aguero limped off the pitch in the first half of Argentina's 3-2 win over Nigeria on Wednesday.
Martinez described the injury as a ''first-degree'' strain in a muscle on the back of his thigh. That means it only affects a few of the muscle fibers but even so it could take several weeks to heal.
Argentina faces Switzerland on Tuesday in Sao Paolo.
''Obviously Sergio is not available for the next match,'' Martinez said. ''From there on it depends on ... Sergio's evolution day by day.''
Earlier Thursday, a team spokesman denied a report by Argentine newspaper Clarin saying Aguero had been ruled out of the tournament because of the injury.
Ezequiel Lavezzi came on for Aguero against Nigeria and is likely to get the nod again if coach Alejandro Sabella sticks to the three-man attack that is Argentina's favored formation.
Aguero wasn't having a great World Cup before the injury, failing to score despite starting in all three group stage matches. Team captain Lionel Messi has scored four of Argentina's six goals so far.
- Sports & Recreation
- Sergio Aguero
- Daniel Martinez