Ireland fly-half Johnny Sexton will be out for 8-10 weeks with a significant medial tear to his right knee.
The likelihood is that the veteran number 10 will miss out on the opener against Scotland on February 1 and the much-anticipated clash with Wales seven days later, both of them at the Aviva Stadium.
The common-sense approach might be to aim for Ireland’s away date with England at Twickenham on February 23.
Even then, there are no guarantees as it will come down to how well Sexton’s battered body reacts to the rehabilitation process.
The injury also effectively rules Sexton out of Farrell’s reckoning for the Irish captaincy, at least in the short term.