Argentina lock Tomas Lavanini will be out of action for six months after damaging his cruciate ligament in the 26-24 Rugby Championship victory over South Africa.
The Jaguares' second row suffered the injury as the Pumas defeated the Springboks in Salta on Saturday.
"Unfortunately, we have just confirmed Tomas Lavanini's injury," Argentina team doctor Guillermo Botto said in a statement on the Argentina Rugby Union website.
"It's a cruciate ligament injury and we expect to do surgery in three to four weeks and then he'll have an estimated recovery time of six months."
Lavanini is joined on the sidelines by wing Manuel Montero, who tore a thigh muscle in the same match.
In the absence of the injured pair, number eight Leonardo Senatore, centres Matias Moroni and Jeronimo de la Fuente and scrum-half Felipe Ezcurra have been selected in Daniel Hourcade's 28-man squad for the Tests against New Zealand and Australia.
According to Botto, fly-half Nicolas Sanchez and centre Juan Martin Hernandez will recover from head injuries in time to feature against the All Blacks in Hamilton on September 10.
Argentina squad in full:
Forwards: Nahuel Tetaz Chaparro, Felipe Arregui, Agustin Creevy (captain), Lucas Noguera Paz, Julian Montoya, Ramiro Herrera, Enrique Pieretto, Matias Alemanno, Guido Petti, Marcos Kremer, Juan Manuel Leguizamon, Pablo Matera, Javier Ortega Desio, Leonardo Senatore, Facundo Isa.
Backs: Martin Landajo, Tomas Cubelli, Felipe Ezcurra, Santiago Gonzalez Iglesias, Nicolas Sanchez, Santiago Cordero, Ramiro Moyano, Jeronimo de la Fuente, Juan Martin Hernandez, Matias Moroni, Matias Orlando, Lucas Gonzalez Amorosino.