Johnny Sexton will miss at least Ireland's first game of the Six Nations
Sexton has 63 caps for Ireland but has struggled with injury and has a history of concussions.
But Ian Keatley is understood to have trained with the Ireland squad yesterday as a precaution before Sexton further injured a troublesome calf.
The 2015 champions will now begin their campaign against Scotland at Murrayfield on Saturday (2.25pm) without their talismanic fly-half.
Paddy Jackson is expected to start in his place.
More to follow.