Agustin Pichot has been named Argentina captain for the World Cup, following the injury that ruled Lisandro Arbizu out of the tournament.
Pichot will be going to his third World Cup
The 29-year-old former Bristol scrum-half was named by coach Marcelo Loffreda on Tuesday in Rosario.
Pichot, who joined French club Stade Francais after leaving Bristol, will be going to his third World Cup - although he did not play in 1995.
Arbizu was ruled out after rupturing ligaments in his right knee in a warm up game, and is being replaced by Martin Gaitan.
The 31-year-old had been hoping to play in his fourth World Cup but his career could now be in doubt.
"I'm at a loss of words," said Arbizu.
"I need to be operated on immediately and after I've recovered I will see what my options are. All I can say is that this will all be a very new challenge for me."
Gaitan, who plays for French side Biarritz, last played for Argentina against the USA last month when he won his fourth cap.
He will join up with the squad on Thursday for their final warm-up match against a regional selection.
Argentina open the World Cup against defending champions Australia on 10 October.