Wales have been forced into making a change among their replacements for Saturday's Test match against Argentina at the Millennium Stadium, with Bradley Davies ruled out with an ankle injury.
The Cardiff Blues lock suffered the knock in training earlier this week, meaning a call-up for Ospreys forward Jonathan Thomas.
"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."
Scarlets full-back Morgan Stoddart, meanwhile, has suffered a torn hamstring that means his autumn series is over.
Stoddart was called into the squad earlier this month, and featured among the substitutes against Samoa last Friday. He did not gain selection for the match-day 22 this weekend.
Davies added: "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."
Wales head coach Warren Gatland and his management team will decide early next week whether to draft in any players ahead of the autumn finale against Australia.