Lavanini's season is over
Both players picked up injuries in during their team's historic 26-24 win over South Africa last weekend.
Lavanini has an anterior cruciate ligament injury and he is expected to have surgery in three to four weeks time. It is then estimated that he will be out of action for up to six months.
Montero suffered a grade one tear in his adductor muscle in his thigh and is expected to be out for a lengthy period as well.
Meanwhile, both Nicolas Sanchez and Juan Martin Hernandez were included in Daniel Hourcade's squad for their Australasian leg of their Rugby Championship campaign.
The duo left the field in Salta against the Springboks with concussion, but both are expected to make a full recovery ahead of the Pumas next match against the All Blacks next weekend.
Leonardo Senatore, Felipe Ezcurra and Jeronimo De la Fuente were also included in the 28-man squad after not playing any part in Argentina's first two games.
Argentina squad:
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, Joaquin Tuculet.
