Pablo Matera was stripped of the Argentina captaincy and suspended with two teammates on Tuesday for historical social media posts deemed to be "discriminatory and xenophobic."
The Argentina Rugby Union said further disciplinary action may be coming.
The sanctions were announced a day after backlash in Argentina for the low-key way the team responded to the death last week of soccer great Diego Maradona.
Matera became a national hero when he led the Pumas to their first win over New Zealand in November in the ongoing Tri Nations series in Australia. Now he, veteran lock Guido Petti and hooker Santiago Socino will miss their final Tri Nations match against Australia on Saturday in Sydney.
The UAR said it "repudiates the discriminatory and xenophobic comments published by members of the Los Pumas team on social networks" from 2011 to 2013.
The statement added the social media posts didn't reflect the personalities of the trio while they have been playing for the Pumas, but "the Argentine Rugby Union condemns all kinds of hate speech and consider unacceptable that those who conveyed them represent our country."
The posts, mostly tweets, reportedly were aimed at Black people and Bolivian and Paraguayan domestic workers.
Matera, who played his first international match in 2013, has closed his Twitter account and expressed regret on Instagram about the messages.