Argentina fullback Juan Cruz Mallia sustained an anterior cruciate ligament injury to his right knee in the loss to England, the team said on Monday.
The 29-year-old was forced off the field late in Sunday's 27-23 defeat at Twickenham after a tackle by England forward Tom Curry that drew the ire of the Pumas.
Argentina coach Felipe Contepomi labelled Curry a "bully" after accusing the flanker of shoving and swearing at him during a tunnel bust-up.
French Top 14 club Toulouse said Mallia would undergo further tests to determine the extent of his injury.