Key midfielder Glenn Whelan damaged a hamstring 20 minutes into Stoke's 0-0 Barclays Premier League draw with Liverpool on Sunday afternoon and will be assessed on Monday when he meets up with the squad in Dublin.
He joins Leicester defender Sean St Ledger and Sunderland winger James McClean on the injured list with striker Kevin Doyle having already been ruled out with a thigh problem.
St Ledger will also have a scan on his hamstring in Ireland on Monday, while McClean's groin will be examined on Wearside after he complained of tightness following Saturday's 3-0 defeat at Manchester City.
A spokesman for the Football Association of Ireland said: "Glenn Whelan came off with a hamstring injury after 20 minutes in Stoke's match against Liverpool today [Sunday].
"He will undergo a scan in Dublin tomorrow [Monday] morning before any further decision is taken on his finess.
"A decision on both Sean St Ledger and James McClean's fitness will also be made tomorrow [Monday] after scans on their respective injuries."
Manchester United winger Robbie Brady, who was initially placed on the stand-by list, has already been drafted into the squad along with Sunderland's David Meyler.
The Republic face Group C favourites Germany at the Aviva Stadium on Friday evening and then head for Torshavn for the clash with the Faroes next Tuesday.
They launched their qualification campaign with an unconvincing 2-1 win in Kazakhstan last month, but will be looking for a significant improvement this time around.