Joe Schmidt revealed that Paul O'Connell is Ireland's biggest injury concern after their bruising win over France in Cardiff.
The Irish skipper was stretchered off at half-time with a hamstring injury, and could have played his final game of Test rugby with this his final tournament.
Schmidt was more optimistic over Johnny Sexton and Peter O'Mahony, who were also forced off during the 24-9 win, with both in contention to feature against Argentina next week.
"I'm incredibly proud of our performance," said Schmidt.
"The update I can give is that it doesn't look great with Paul. It looks like an upper hamstring. But we're probably going to have to wait until tomorrow to get that scanned.
"Johnny it looked like an adductor to me but that's not the learned eye of a medic. We're probably going to get Johnny scanned tomorrow and Pete O'Mahony as well.
"Pete didn't seem too bad so we're hopeful with Pete. I think it's a twist of the ankle or knee. But he was walking pretty well in the changing room and hopefully he's going to be ok.
"I've spoken briefly to Johnny and he's already talking about next week. I'm not sure whether that means he'll be playing or not. It's probably Paul who worries me the most of those three."
Schmidt is also optimistic that Sean O'Brien will escape censure for an early punch on Pascal Papé in the opening exchanges. The Irish flanker appeared to catch Papé flush in the ribs off the ball, and Schmidt admits his absence would be a huge blow if he's cited.
Asked if he expected O'Brien would be banned, he replied: "I truly hope not. I think he was being held at the time and he swung.
"I don't think he's looking directly at the player but it's not for me to determine. I also think it's not a closed fist, I'd be hopeful but it's not a decision for me. It's hopefully not something that impacts on us.
"Considering the dressing room at the moment with the amount of injuries we have, we can ill-afford to lose another player, particularly a player of Sean's experience and standing within the group."