Fernandez Lobbe misses the match in Mendoza having left for France where he plays his club rugby for Toulon to meet his newly-born second son.
With Juan Manuel Leguizamon still injured, the Pumas will field a new-look back row as they seek their first win at the close of their third season in the southern hemisphere championship.
Another change coach Daniel Hourcade announced on Tuesday in the forwards has tighthead prop Ramiro Herrera dropping to the bench to be replaced by Nahuel Tetaz Chaparro.
There are three changes in the backs from the side beaten 34-13 by champions New Zealand last Saturday with Martin Landajo coming back at scrumhalf and Tomas Cubelli returning to the bench.
Horacio Agulla, who scored Argentina's consolation try as a replacement last weekend, comes in at outside centre with Marcelo Bosch dropping to the bench and Lucas Gonzalez Amorosino replaces Manuel Montero on the left wing.
"We've tried to balance the physical aspect without altering the team structure too much," Hourcade said.
"There are players who have had a long year and played almost every minute in the tournament and are starting to feel the wear and tear of such a demanding competition.
"We hope to play our best match of the tournament for a great finish. Australia have already shown us the class of rivals they are and it will surely be a big challenge for us."
Argentina lost 32-25 to Australia at Gold Cost on September 13 earning the third of their three bonus points.
Team: 15-Joaquin Tuculet, 14-Juan Imhoff, 13-Horacio Agulla, 12-Juan Martin Hernandez, 11-Lucas Gonzalez Amorosino, 10-Nicolas Sanchez, 9-Martin Landajo; 8-Leonardo Senatore, 7-Benjamin Macome, 6-Rodrigo Baez, 5-Tomas Lavanini, 4-Mariano Galarza, 3-Nahuel Tetaz Chaparro, 2-Agustin Creevy (captain), 1-Marcos Ayerza
Replacements: 16-Matias Cortese, 17-Bruno Postiglioni, 18-Ramiro Herrera, 19-Matias Alemanno, 20-Javier Ortega Desio, 21-Thomas Cubelli, 22-Marcelo Bosch, 23-Jeronimo De la Fuente