(Adds update from team doctor)
By Marcelo Andreotto
BELO HORIZONTE, Brazil, June 26 (Reuters) - Argentina striker Sergio Aguero will miss the upcoming last 16 clash with Switzerland after suffering a muscle injury in his left leg and could be out of the World Cup should they progress.
Aguero's injury in the 3-2 victory over Nigeria on Wednesday is a major blow to the South Americans' campaign to capture a third World Cup, this time on the soil of their great rivals Brazil.
Team doctor Daniel Martinez told reporters the 26-year-old was undergoing magnetic resonance and other urgent treatments at the team's camp in Belo Horizonte.
"We have available all the resources to progress as quickly as possible," he said. "He won't be ready for the Switzerland game, and from there we'll check his evolution day-by-day."
Other sources close to the team said Aguero would almost certainly also be out for further games assuming Argentina progress.
The Manchester City forward, part of Argentina's so-called "Fab Four" of strikers, was taken off during the first half of the match against Nigeria that gave them top spot in Group F.
Nicknamed "Kun" after a Japanese cartoon character, Aguero is a close friend of national captain Lionel Messi and is also the father of Diego Maradona's first grandson.
Argentina play Switzerland in Sao Paulo on Tuesday.
"We have forwards of the same style as Aguero and others, with a different style, like Lavezzi, who came in and handled himself well on the wings and helped us cover spaces," coach Alejandro Sabella said after the Nigeria game, where Lavezzi replaced Aguero. (Additional reporting by Andrew Cawthorne; editing by Justin Palmer)