Keogh was set to lead the Irish in the game against Scotland last Tuesday but pulled out just before kick-off with the back injury and his place went to John Muldoon. It was hoped that the injury would respond to treatment but that hasn't been the case and Keogh will take no further part in the tournament.
The Irish management have called up Jody Danagher the Ul Bohemians prop to replace Keogh. The move to substitute a front-row forward for a back-rower is explained by team manager David Haslett who said, "We are happy enough that we have sufficient cover in the squad to cover for Stephen and so have opted to bring in Jody to bolster our front row for what will be very physically demanding games ahead.
"Of course it's a blow to lose Stephen. He's the captain and besides is a vastly experienced player. And coming as it does having already lost John Lyne it certainly doesn't make things any easier. But we will cope, I have no doubt about that."
The first thing they'll have to cope with is the Argentinians on Saturday. The task facing the Irish is clear cut. They must win and get themselves a bonus point against Argentina. If they achieve that then they'll cast an anxious glance towards Newbury where Wales will be in action against South Africa with the Irish hoping that the Baby Boks can inflict a comprehensive defeat on the Six Nations Champions.