O'Brien's injury deals Ireland devastating World Cup blow
Joe Schmidt will name his squad for the World Cup in the next 48 hours. However, prior to his players embarking on their short, well-earned break before re-assembling for pre-season in mid-June, he has already lost two key figures in his back-row.
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Yesterday's confirmation that Seán O'Brien's hip injury needs surgery and will keep him sidelined for six months was a devastating blow to a great player whose Ireland career looks to have finished on 56 caps at the age of 32.
On Saturday, he lifted the Guinness PRO14 trophy in his club suit, but his Leinster career is at an end and he goes to London Irish on the back of a long lay-off and with major doubts over his durability after an injury ridden couple of seasons since his starring role on the 2017 Lions tour.
Although there were flashes of brilliance, O'Brien would admit that he hasn't been himself this season.
Even still, his is a name that commands real respect across the rugby world and, in particular, in New Zealand where his performances earned him that rarest of accolades; name-recognition.
Losing Dan Leavy, O'Brien's natural heir, was unfortunate but to lose the two toughest opensides on the roster is a major blow for Schmidt to take.
Suddenly, Josh van der Flier is the most important player in Irish rugby.
Quality opensides are a rare commodity and Ireland are lucky to have a couple, but injuries are making that pool dangerously shallow.
In 2015, Schmidt's frontline back-rows all went to Japan but he lost his cover in the build-up and, when Peter O'Mahony and O'Brien were unavailable for the quarter-final, he paid the price. Now, he faces a similar scenario.
The coach has steadily built the depth across most positions, but no team can sustain the loss of a number of players in the same position.
Schmidt does have options, but the loss of Leavy and O'Brien limits the team's physical prowess and will possibly force them to re-think their approach.
With warm-up games against Italy, England twice and Wales before a congested pool schedule that sees Ireland take on Scotland and Japan, before two bruising fixtures against Russia and Samoa leading into a likely quarter-final against New Zealand or South Africa, there is a high chance of another back-rower suffering injury.
The openside stocks are now down to van der Flier, Jordi Murphy, Jack O'Donoghue and Sean Reidy, with Connacht's Paul Boyle and Leinster's Max Deegan and Scott Penny outside contenders. Munster's Tommy O'Donnell is something of a forgotten man but he can't be discounted either. CJ Stander started there for Munster last weekend and may get another look.
On paper, it may look like Schmidt has depth but the reality is that Leavy and O'Brien are generational talents whose abilities, at their best, set them apart from the field.
Schmidt's Ireland have a ruthless attitude to injury and a strong record of getting on with the job, but their chances of winning the World Cup have been diminished by these early injuries.
That's the team's loss. For O'Brien himself, this must be a devastating blow.
Although injury has deprived the Tullow Tank of another half-century of caps, his greatest moments in green have come at World Cups.
In 2011, he was one of the stars of the tournament and four years later he was sensational against France. Unfortunately, a rash gut-punch on Paschal Papé deprived him of his chance at the quarter-final.
When his one-week ban was up, Ireland were already gone.
For all that this has been a difficult few months, there was always a sense that a good pre-season could get him back to his best in time for the tournament.
Maybe it was the nostalgia talking, but his displays on the 2017 tour are too recent to dismiss. He was sensational in New Zealand and unlucky not to win Player of the Series.
For London Irish, though, there must be worry about the ability of their marquee signing to live up to his name.