Brian O'Driscoll remains in contention to play for Ireland against France on Sunday after he underwent a scan on his hamstring injury on Monday.
The Irish RFU said that O'Driscoll had suffered a "mild strain" in Sunday's win over Wales and that the injury was "not as serious as first feared".
However, Peter Stringer is now also a major fitness worry for the game.
The scrum-half suffered a hairline fracture to a bone in his right hand in Sunday's win over Wales.
If Stringer is ruled out, Ulster's Isaac Boss would be in line to start against France.
The IRFU statement said that O'Driscoll would undergo a rehabilitation programme this week and that a further medical update would be made on Saturday, 24 hours before the Croke Park contest.
Stringer will not train in the early part of this week but the IRFU said that he had not been ruled out of selection for this weekend's game.
Gordon D'Arcy suffered a groin strain during the early stages of the game in Cardiff but the injury has responded well to treatment and he is expected to be available for selection.
Denis Leamy had an abscess incised and drained on Monday and he is expected to be fit for Sunday's game.
Ulster's Tommy Bowe and Bryan Young are among 10 players brought into the Ireland squad as cover.
Bowe, Rob Kearney, Barry Murphy, Kieran Lewis and Eoin Reddan are added as backs cover while fit-again Malcolm O'Kelly, Jamie Heaslip, Keith Gleeson, Trevor Hogan and Young are drafted into the forwards.
O'Driscoll initially felt the injury earlier in the second half when supporting a break from Ronan O'Gara but continued after receiving treatment.
If O'Driscoll is ruled out, Andrew Trimble would be expected to switch to centre with Geordan Murphy coming into the starting line-up.