No player is ever irreplaceable, but when it comes to Leinster and Irish rugby, Brian O'Driscoll is mighty close. Can Ireland beat the Boks or pip the Pumas in next month's games without him? Perhaps, but one thing's for sure: it's going to be a damn sight harder in the gifted one's absence.
Declan Kidney has been robbed of two of his squad's central characters. The skipper and Rory Best are among Kidney's most reliable on-field leaders -- commanding players who never, ever shirk responsibility.
There are certain individuals whose mere presence in the team elicits the best in others. O'Driscoll is to rugby what Henry Shefflin is to hurling, a colossus in word and deed.
A few days ago I suggested that Ireland should be targeting nothing less than a clean sweep of victories in the November internationals, irrespective of the grizzled opposition.
He may not have been shouting it from the rooftops, but I know that one our greatest ever players agreed.
O'Driscoll was hurt badly by what happened in Hamilton in June and had been counting the days until November 10 to get the chance to redeem that awful loss.
Nothing can remove that All Black blemish from his CV, but beating South Africa would have represented a huge step in exorcising the demons of that hammering.
On Saturday, before he turned his ankle against Cardiff at the RDS, he was on fire. Whenever O'Driscoll hits this level of performance the rest follow.
But O'Driscoll is an enormous loss and Leinster's back-to-back games with Clermont take on an entirely different perspective now.
As for Kidney and Ireland, the challenge now is to reshuffle a backline which, had Rob Kearney and O'Driscoll been available, effectively would have picked itself.
If Keith Earls is deemed fit then I think Kidney should give the Moyross man the No 13 shirt -- the position in which he is most happy.
Whether or not that will transpire will of course depend on the call at full-back.
For Kidney and his management, it is one almighty nightmare. Tommy Bowe is being bandied about as a possible option for full-back, and he could also fill the outside-centre void as it is a position he occasionally played in for the Ospreys.
Young Ulster centres Luke Marshall or Darren Cave don't look ready to make the step up just yet. Beyond a fully-fit Earls, McFadden would be the logical choice alongside Gordon D'Arcy on the basis of experience and form -- although admittedly he's shown the latter primarily on the wing.
The hooking situation is a lot easier to manage, with Richardt Strauss and Sean Cronin one and two, leaving it a toss-up between the Munster pair of Mike Sherry and Damien Varley for the standby call.
A backline that looked set in stone now seems set to challenge the management think-tank like never before. Who will be full-back? Where will Bowe play? Who will be scrum-half? And what about Earls?
As of now take Jonny Sexton to wear 10 and D'Arcy alongside at 12, but after that there are so many permutations.
It's been a bad few days for Irish rugby. God forbid that anything untoward should happen to Paul O'Connell!