The surgery nearly certainly rules O'Brien out for Ireland's opening game of the Six Nations against France in Paris on February, and given the nature of the injury so far, it's unclear as to how long it will take for him to get back to full fitness, athough Leinster have said that the aim, at least, is for him to return at some point during the tournament.
With the treatment proving unsuccessful, the decision was made for O'Brien to go under the knife.
Leinster say the target is to have O'Brien back available "during the Six Nations window", which has raised further doubts over whether he'll be fit to play any part during the championship.
Marido de Anitta opina sobre as roupas curtas da cantora
Querida conta fake criada para externar seus pensamentos sem sofrer consequências, se você soubesse de 1/3 do que se passa. Thiago sempre foi apontado como discreto por Anitta . "A relação deles é de amizade.
O'Brien, therefore, looks set to miss Ireland's Six Nations opener in France on 3 February but could return later in the tournament.
During that period, Leinster have Guinness Pro14 games against Edinburgh, Scarlets and the Kings.
Leinster say a return to play timeline for Byrne, who hasn't played since making his global debut against Argentina in November, will be formalised post-surgery.
FO summons Indian diplomat over ceasefire violations
The Foreign Office told the Indian diplomat that despite calls for restraint, India continued to indulge in ceasefire violations. Islamabad says Thursday's shooting was the latest cease-fire violation by India in the village of Kot Kotera.
Cullen could provide further updates on both O'Brien and fellow Ireland worldwide Adam Byrne - who is also due to undergo a procedure to correct a knee injury picked up in the November internationals - when he speaks to the media on Friday afternoon.
Leinster will name their team for the Glasgow game later this afternoon, with Leo Cullen expected to speak to the press with more details about O'Brien's situation.
The42 has just published its first book, Behind The Lines, a collection of some of the year's best sports stories.
Sacred traditions stop ANC leaders from paying tribute at Qunu
Although Magashule did not disclose the details, the talks were believed to be part of the process of persuading Zuma to resign. Earlier, several NEC members almost missed out on the meeting as security at the Mandela homestead did not recognise them.