Wales are sweating on the fitness of two of their marquee players, centre Jamie Roberts and lock Alun Wyn Jones, in the wake of their 26-12 defeat to Argentina at the Millennium Stadium.
Roberts lasted 22 minutes before being laid out in a sickening clash of heads, while Jones damaged his left shoulder in a collision with opposite number Manuel Carriza in the second half.
"Jamie has mild concussion - to say the least - and Alun Wyn has done his AC (joint capsule in collarbone) and right now it does not look good. It is certainly going to test the strength in depth of our squad," said Wales interim head coach Rob Howley.
It was the fourth defeat in a row for the 2012 Grand Slam champions, who now have to face Samoa on Friday night before tackling New Zealand and Australia.
"I'm disappointed, frustrated and annoyed," admitted Howley, "but we will dust ourselves off and look forward to the Samoan challenge on Friday night.
"There is no doubt that Argentina have gained the experience of their exposure in the Rugby Championship against New Zealand, South Africa and Australia and that showed in the way they played the game.
"We looked to be in second gear and the last 30 minutes were hugely disappointing.
We trained particularly well leading up to the game but the Rugby Championship has taken this Argentine side to another level in tempo, pace and intensity and we very much came second.
"Obviously this is a set-back but we have three more games to go and plenty to play for - it is important we go into those matches with self belief and confidence.
"History suggests that Wales get stronger as the autumn series goes on and I am sure that will happen. We've got three games to go, a hugely physical challenge with Samoa next week so it's important we get back on the training paddock and sort things out.
"International rugby is about scoring tries. It hasn't been a problem for us in the recent past but today as I say, we struggled with possession and territory.
"That was an area of concern in terms of struggling with territory and possession and not being able to put Argentina under the pressure we wanted them to, particularly in their 22 metre area.
"We have to work hard and be smart and there were areas today where we weren't smart. We have to improve all round."
Wales captain Sam Warburton added that "basic errors hurt us quite a bit and we did not start the second half very well at all" while opposite number Juan Martin Fernandez Lobbe heralded his side's triumph as a major step forward.
"This is a great win for us, a win we've been searching for as a new group. It's a huge honour to get that first win in such a lovely stadium - the best stadium in the world," said Fernandez Lobbe.
"For us the most important thing was to get that win and we're so happy to do that against such a good team, the Six Nations champions."