Argentina v IrelandInjured full-back Girvan Dempsey is out of Ireland's crunch game with Argentina on Sunday with Geordan Murphy called-up for his first World Cup start.
Coach Eddie O'Sullivan has not been panicked into making a raft of changes although he brings in Denis Hickie for Andrew Trimble on the left wing.
O'Sullivan has not tinkered with the pack but there is a worry over the injury to Jerry Flannery's shoulder.
Rory Best, however, could be forced into a quicker than expected return.
Best fractured his thumb against Georgia and was expected to be ruled out of the remaining Pool D games.
However, the Ulster hooker could be called upon if Flannery's injury does not fully recover.
Irish coach Eddie O'Sullivan explained that Murphy's inclusion was not due to Dempsey's absence.
"Geordan would have been included in the back three anyway - he has the kind of attacking edge we need this weekend," he said.
"The roles are reversed with Denis (Hickie) in for Andrew (Trimble).
"The selections from last week and for this week were based on what we were expecting from France and now Argentina. It was a tight selection call between them.
"I'm pretty happy with the back three. There's a lot of experience in it and a lot of strike power and hopefully it will come into play on Sunday."
Dempsey received his injury during the defeat by France last Friday, and was ruled out on Monday evening.
Murphy's only other appearance during this World Cup was a 30-second cameo in Ireland's Lethargic win over Namibia.
He was controversially dropped from the 22-man squad for the French game with Gavin Duffy brought onto the bench. Duffy now makes way for Trimble who can cover centre and wing.
This could well be Hickie's final international game as he is due to retire following the World Cup.
Ireland need to score four or more tries against Argentina and defeat them by more than seven points to go through to the quarter-final stage.
Argentina have so far not had their line crossed during the present campaign and officially have the most miserly defence in the tournament.
Ireland: Murphy; Horgan, O'Driscoll, D'Arcy, Hickie; O'Gara, Reddan; Horan, A N Other, Hayes, O'Callaghan, O'Connell, Easterby, D. Wallace, Leamy.
Replacements: A N Other, S Best, O'Kelly, N Best, Boss, P Wallace, A Trimble.
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