Also withdrawn from the squad this week is Scarlets back Morgan Stoddart, who has picked up a hamstring tear which will see him in rehabilitation for up to four weeks.
"Bradley suffered a ligament sprain to his ankle during training on Tuesday and subsequently has been pulled out of the match against the Pumas this weekend," said Wales physiotherapist Mark Davies.
"He will remain in camp and his progress will be reviewed early next week before a final assessment is made.
"Morgan has a grade two tear to his hamstring and he will now be in recovery and rehab for a period of up to four weeks."
The Wales management team will take a decision on whether or not to call any further personnel into the Invesco Perpetual Series squad early next week.
Jonathan THOMAS (OSPREYS - Cap No 1,013)
DoB: 27.12.82. 6'5" / 1.96m. 17st 5lbs / 110kgs
International record: 48 caps (W 24, L 22, D 2; 35 pts - 7T)