Jaguares take rookie prop to South Africa
The 22-year-old Diaz replaces Argentina international Santiago García Botta.
Diaz had a short stint with French side Stade Francais before returning to local Argentian side Belgrano Athletic Club in 2015.
The youngster has six caps for the national side and was a late call-up for the Los Pumas in the 2015 World Cup.
The side will be captain by Pablo Matera while Joaquín Tuculet and Tomás Lezana will fulfil the roles of sub captains.
"The inclusion of Javier Díaz is because Santiago García-Botta can't make the trip," coach Ledesma revealed.
"The first list is always very difficult and very complicated because we have to leave players out. I think the next squad will be easier because there will be other factors to take into considerations,"
Jaguares will head to South Africa on Wednesday where they will play two Super Rugby games against the Stormers on February 17 and Lions a week later.
Jaguares: Matias Alemanno, Felipe Arregui, Gonzala Bertranou, Emiliano Boffelli, Sebastian Cancelliere, Agustin Creevy, Bautista Delguy, Javier Diaz, Joaquin Dian Bonilla, Bautista Ezcurra, Santiago Gonzales Iglesias, Juan Martin Hernandez, Marco Kremer, Martin Landajo, Tomas Lavanni, Juan Manuel Leguizamon, Nicolas Leiva, Tomas Lezana, Pablo Matera, Julian Montoya, Ramiro Moyano, Matias Orlando, Javier Ortega Desio, Guido Petti, Nicolas Sanchez, Leonardo Senatore, Nahuel Tates Chaparro, Joaquin Tuculet, Juan Pablo Zeiss