Keith Earls suffered a suspected concussion in Ireland's 16-16 RBS 6 Nations draw with Wales and could miss the second-round clash in France.
The Munster flyer must now go through the return to play protocols to prove his fitness for Ireland's Stade de France match in Paris on Saturday.
Flanker Tommy O'Donnell passed a Head Injury Assessment (HIA), so will be free to return to training, while fly-half Johnny Sexton avoided serious injury despite suffering a "sore" bang to his chest, Ireland boss Joe Schmidt confirmed.
"Tommy O'Donnell passed his HIA and showed no ill effects," said Schmidt. "He could have returned to play but by then Rhys Ruddock had slotted in and was comfortable. So we thought we would leave it at that.
"Keith has probably suffered a concussion. He will be considered to have had a concussive impact and that will certainly put him in doubt for next weekend.
"Johnny is sore without a doubt, but I was just talking to Jonathan Davies in the corridor and he's sore too. There are definitely a few sore bodies after a game like that."
Ireland boss Schmidt expects to have full-back Rob Kearney and Sean O'Brien available for selection to face France after both Leinster stars missed the Wales draw with hamstring problems.
"Sean could potentially have gone onto the pitch today," he said. "But we also know that would have been an exacerbative risk. But I thought the guys who stepped into position did really well."
No team has ever won the Six Nations with a draw en route, but Ireland boss Schmidt still believes his side can take the title.
Ireland would set a new precedent with a third consecutive Six Nations crown in any case, and Schmidt said his players can ill afford to be distracted by thoughts of glory.
"I can see why that stat exists, because it's such a tough competition," said Schmidt. "It's one of a number of worrying things that we've got to overcome.
"It won't affect our recovery and our preparation to face France. It will be a monumental task to compete with France."
Fly-half Sexton posted the match-levelling penalty while fending off the blow to the chest that saw him withdrawn moments later.
"His [Sexton's] mental strength is such that it's not something I'd have too many second-thoughts about," said Schmidt. "We made the substitution post the kick, but we probably would have made it anyway to save him a bit for next week.
"I feel encouraged after the performance. As much as you're always disappointed not to get the result, I thought the performance stood to the players really well."