Argentina star Juan Martin Hernandez will miss the World Cup after failing to recover in time from a knee injury.
The 28-year-old, who plays for French club side Racing Metro, underwent a knee ligament operation in March.
Argentina play England in Dunedin on 10 September in their opening World Cup fixture, with Scotland also in Group B.
"He made a great effort to get there but in our heads it was as if he wasn't going to be with us," said Pumas coach Santiago Phelan.
"It would have been a plus. This doesn't take away (the fact) that it's an important loss for his qualities as a player and a person."
Hernandez plays at fly-half for Racing Metro but has regularly featured at full-back, and he was a key member of the Argentina side that finished third at the last World Cup in France.
Phelan has selected 10 veterans of the 2007 tournament including centre Felipe Contepomi, who will captain a squad featuring 25 players who play their club rugby in Europe, 20 in France and five in England.
The Premiership quintet are Leicester duo Marcos Ayerza and Horacio Agulla, Harlequins lock Tomas Vallejos, Exeter wing Gonzalo Camacho and London Irish scrum-half Alfredo Lalanne.
Argentina play Wales in Cardiff on 20 August as their last warm-up match before the tournament begins in New Zealand.
Forwards: Juan Fernandez Lobbe (Toulon), Juan Manuel Leguizamon (Lyon), Leonardo Senatore (Gimnasia Rosario), Alejandro Campos (Agen), Alvaro Galindo (Racing Metro), Patricio Albacete (Toulouse), Manuel Carizza (Biarritz), Julio Farias Cabello (Tucuman RC), Mariano Galarza (unattached), Tomas Vallejos (Harlequins), Marcos Ayerza (Leicester Tigers), Agustin Creevy (Montpellier), Juan Figallo (Montpellier), Maximiliano Bustos (Montpellier), Mario Ledesma (Clermont), Rodrigo Roncero (Stade Francais), Martin Scelzo (Agen)
Backs: Martin Rodriguez (Stade Francais), Horacio Agulla (Leicester Tigers), Juan Jose Imhoff (Duendes), Gonzalo Camacho (Exeter), Lucas Gonzalez Amorosino (Montpellier), Agustin Gosio (Newman), Gonzalo Tiesi (Stade Francais), Santiago Fernandez (Montpellier), Marcelo Bosch (Biarritz), Felipe Contepomi (Stade Francais, captain), Nicolas Sanchez (Bordeaux-Begles), Alfredo Lalanne (London Irish), Nicolas Vergallo (Toulouse).