|Captain Brian O'Driscoll|
O'Driscoll's absence was expected, after he suffered a long-term injury earlier this season, but nonetheless the former captain will still be missed. Despite being 32 years of age, O'Driscoll still figured to be a key player in Ireland's hopes to land another Grand Slam under Kidney.
Without him, there is a gap at the outside center position that has not had to be filled by anyone other than the Leinster man in a long time.
O'Driscoll has been the one constant in the Irish team since 2000 after breaking into the team at a young age and continuing his world class play until last year's world cup.
Kidney's squad has been compromised in a fashion that presents multiple options for the head coach to replace the eighth highest try scorer in Rugby Union history.
The long-time center partner of O'Driscoll, Gordon D'Arcy, is available and in the squad but whether he still merits a place in the starting line-up isn't clear.
D'Arcy's level of play has been nowhere near expectations for an international center over the past few years. Now that O'Driscoll is out, it may be a good time to establish a new center pairing completely, at least for this competition, before bringing back the former captain.
Because of the versatility of many players picked in the squad, there is not really a true center in line to replace either D'Arcy or O'Driscoll, but instead a slew of players who play multiple positions.
Keith Earls has proven himself as a game changing outside center in the 13 shirt for Munster at the provincial level. However he has yet to fully ignite his international career. An extended stint in O'Driscoll's spot could see him rise to meet his potential.
Earls is no longer a youngster at 24 years of age. He has the experience internationally and should be expecting to contribute more at this level this year. He would bring the explosion and speed of a young O'Driscoll without the tenacity in defense or ability to compete in rucks like a flanker.
Truly, there is no possible way to completely replace what O'Driscoll brought to the team with just one player.
No other player in the history of the game brought such an all-around game from the center position. Everyone could see his ability to beat defenders and score tries, but his all-around game is what set him apart and allowed his career to extend over a decade.
The subtle passes, intelligent interceptions, timely turnovers on the ground and reading of situations in the centre that he possessed, and possesses still, isn't something that can be replicated.
Earls inclusion would bring more explosion to the Irish back-line and should he be the team's starter, then it would be considered the most aggressive move that Declan Kidney could make.
Earls' best position is difficult to determine because of his consistency both on the wing and inside, while also showing flashes as a fullback in the past. Kidney may favor playing him on the wing which would open up the door for either Fergus McFadden or Andrew Trimble to move inside.
Both McFadden and Trimble have spent more time on the wing internationally, but both have also played center in the past also. Even though Kidney has used Earls in the center ahead of those two previously, that doesn't guarantee that one of the duo could push him out.
Kidney has never given anyone anything for past achievements, if he did work that way, Luke Fitzgerald would be in the squad still.
Trimble and McFadden are bigger than Earls and wold provide a greater physical presence in defense. McFadden has the capabilities to play the 12 position, and wold be closer to the all-around player that O'Driscoll is, but Trimble is a big hitter who can repeatedly pound against the opposition and finish with precision.
McFadden's versatility, as well as Paddy Wallace's good play for Ulster this year, is what is threatening Gordon D'Arcy's starting spot. McFadden and Wallace both have the intelligence and passing ability to play 12 which gives Kidney more decisions to make in the middle of the field.
Whether it be McFadden and Earls, Wallace and Earls or either of the pair with Trimble, Ireland have proven players to play center instead of Brian O'Driscoll, if not proven centers at least.
If Kidney really wants to be innovative opposed to aggressive, the option is there for Jonathathan Sexton to slide across and play 12 with Ronan O'Gara starting at 10. This would ease the pressure on him to make a decision between his two star out-halfs while allowing him to get his best players on the field.
Sexton has played first center before, before Felipe Contepomi left for France, he played there for Leinster, while Kidney has experimented with the idea previously in limited action for Ireland.
The biggest worry about playing two out-halfs is the lack of impact on the ground and defensive consistency. Defensively, Sexton is arguably better than D'Arcy playing the 12 position considering the amount of tackles D'Arcy has missed in recent times.
He understands how to play the position and gets himself in the right position to make tackles and support his backline.
Sexton's presence at 12 would put greater pressure on Ireland's back three in the pack to win the ball on the ground. Losing both D'Arcy and O'Driscoll would undoubtedly take away from the team's overall ability to compete in rucks around the field.
Fortunately for Ireland, they have arguably the most talented group of back-row forwards in the world. Asking Stephen Ferris, Jamie Heaslip and Sean O'Brien to do more is no problem.
With Sexton inside, the likelihood is that Fergus McFadden or Keith Earls would be preferred at 13 opposed to Trimble. For the simple reason that McFadden and Earls have more experience playing the position than Trimble, who has spent most of his career, both provincially and internationally, on the wing.
Starting two out-halfs would drastically impact Ireland's gameplan, however, it wouldn't limit Ireland's explosiveness. Both Sexton and O'Gara can pass the ball as well as anyone while Sexton isn't the type of player that defenders can ignore running with the ball.
Tommy Bowe, Rob Kearney and whoever starts on the opposite wing, will still be able to expect plenty of opportunities in green jerseys over the coming weeks and months regardless of Brian O'Driscoll's absence.