Sean O'Brien's latest injury setback -- his fourth significant injury in less than a year -- is a devastating blow for club and country but, particularly, it couldn't come at a more inopportune moment for the player himself.
Not only will the Carlow man miss Leinster's crucial concluding Heineken Cup pool matches, wherein they will be striving desperately for a lucrative home quarter-final, he will also be shattered to miss Joe Schmidt's first Six Nations campaign.
And, as time ticks down on his contract negotiations with an assorted clutch of purported suitors, his representatives will now certainly have less wriggle room.
WHAT IT MEANS FOR SEAN O'BRIEN
This latest injury obstacle is a devastating personal and professional blow for one of Irish rugby's most personable players off the field and the most destructive of forces on it.
He played throughout the last Six Nations with a thumb injury and, having overcome a knee injury on the Lions tour, he has been dogged by ankle trouble during what was already a badly disrupted season with injury woes before Saturday's horrific interruption -- he has also suffered ongoing hip problems.
Now he will be sidelined for the most pivotal moments of Heineken Cup qualification for a Leinster side who are still far from guaranteed their quarter-final berth; aside from a winnable game against Ospreys, a visit to Castres in 12 days' time presents a considerable obstacle to his side's chances of sealing a knockout berth.
As for his international commitments, Ireland are already rated as only the fourth most likely team to win the Six Nations, and O'Brien's removal from the squad will surely lengthen their odds.
Few Irish players can command the level of respect and awe engendered by the 'Tullow Tank' and his destructive ball-carrying capabilities. His breakdown work and superb attacking link play, all evidenced in a wondrous performance last month against the All Blacks, will be sorely missed by Ireland coach Schmidt.
In terms of his contract negotiations, his injury provides an unwanted twist. O'Brien needs only to call his team-mate Luke Fitzgerald to view the IRFU's attitude to players with recidivist injury problems.
And, if French clubs were already wary of the predictably protracted poker game being played in his negotiations, a potential season-ending injury may dramatically reduce their interest in a player who will spend more of this season in rehab than in training.
It all adds up to a considerable period of anguish for the 26-year-old who, even if he was veering towards a decision to remain in this country, will do so without being able to contribute on the field for the foreseeable future -- and potentially with less money in his pocket than he was hoping for.
What he admits is a "selfish decision" may now be taken out of his hands.
WHAT IT MEANS FOR LEINSTER
LEINSTER ARE IN THE MIDST OF SOME TURBULENT CHANGE AS, PIECE BY PIECE, THE EXTRAORDINARY SQUAD THAT WON THREE HEINEKEN CUP TITLES DURING FOUR YEARS OF UNPRECEDENTED EUROPEAN DOMINATION IS BEING ERODED.
Schmidt's departure as coach coincided with the exits of Isa Nacewa and Johnny Sexton while, at the end of this season, Brian O'Driscoll and Leo Cullen will retire.
That Leinster are coping so admirably with such an exodus of talent, experience and leadership reflects well on the culture of the club -- now they must fill O'Brien's considerable boots, all the while wary that both he and Jamie Heaslip may not be around at all next season.
Last Saturday's facile win against a poor Ulster side offered another glimpse of the intermittent signs of the bubbling talent on the roster that lies beneath the established world-class stars.
Dominic Ryan has suffered more than most Leinster players with repeated injury setbacks but when he replaced O'Brien for the final half-hour at the RDS last Saturday, he reminded the few who needed convincing that he has all the attributes required to slot in at No 7.
Shane Jennings, likely to come straight into the side for this weekend's trip to Connacht, is still a valuable component of the squad and his leadership capabilities and desire remain as strong as ever.
Kevin McLaughlin has been deservedly edged out of the Heineken Cup equation by Rhys Ruddock's barnstorming form at blindside but he is also a possible option to fill in at No 7.
Looking down the track, should Leinster have the breathing space later this season, coach Matt O'Connor will certainly contemplate affording the exciting and multi-talented Dan Leavy an opportunity to show his burgeoning potential.
However, there is no escaping the conclusion that, regardless of all the available surrogates, O'Brien's absence is incalculable.
WHAT IT MEANS FOR IRELAND
When Schmidt surveyed the traumatic replays of Ireland's last-gasp defeat against the All Blacks, he would have been reminded of the value to his playing philosophy of O'Brien's trademark explosiveness.
Even more valuable was O'Brien's post-match studious commitment to the characteristic ruthlessness of his coach when reflecting on what was, after all, another defeat to the All Blacks.
While other players predictably skirted the topic, O'Brien launched a stunning broadside at the lack of belief within an Ireland squad that had yet again fallen short on a big occasion.
As a demonstration of leadership, it was just as influential as his magnificent performance.
Sadly Schmidt, who relied on O'Brien's ability to break the gain-line in order to develop incisive attacking patterns, will now have to plan without his talisman.
Schmidt's problem is that the leading candidates are themselves struggling with injury -- if he had to pick a team for this weekend, he would probably be forced to switch Peter O'Mahony to the openside.
However, both Ulster's Chris Henry, of whose energetic and accurate work Schmidt is a big fan, and Munster's Tommy O'Donnell are potentially on the brink of comebacks.
Events in Ravenhill this Friday could be hugely significant in the battle for the No 7 jersey against Scotland in February.
O'Donnell represents the nearest facsimile to O'Brien given the ball-carrying abilities that he has displayed in red and, with Heaslip refitting his own profile as a No 8, Schmidt may need all the ball-carriers he can get.
Henry is less of a carrier, more of a workhorse and an enthusiastic scrapper and Schmidt may have to redesign Heaslip's modus operandi or, alternatively, ask O'Mahony to assume more ball-carrying duties.
Sean Dougall has been in good form and he will have something to say about the openside joust with O'Donnell in Munster but the latter would seem to be the preferred option, once fully fit.
Of course, Schmidt could re-calibrate the back-row entirely by selecting Iain Henderson -- another due for a weekend comeback -- on the blindside and moving O'Mahony to the openside but would this skew the balance of the back-row more towards carriers than ball-winners?
Ulster's Grand Slam winner Stephen Ferris has not played rugby in 13 months and is nowhere near a competitive comeback, a reminder that even the cosseted IRFU player welfare programme is no protection against dreaded injury.
It is a huge headache for the Irish coach, but then he knew that would be the case the moment he saw O'Brien disconsolately troop towards the sidelines last Saturday night.