Rory Best has been ruled out of Ireland's match with South Africa at Aviva Stadium on Saturday.
Following a medical review, the decision was taken by the Ireland management team not not to risk Best for the opening clash of the Autumn series.
Best's calf strain has been slower to heal than expected.
He is partaking in modified training but will not feature on Saturday and his progress will continue to be monitored.
Leinster forward Sean Cronin is now likely to start after 32-year-old Best became Ireland's latest front-row injury casualty following props Cian Healy, Martin Moore and Nathan White.
Tighthead prop Mike Ross, meanwhile, is battling to be fit after a month out with groin trouble, although he returned to training on Tuesday.
"Following a medical review yesterday evening, Rory has been ruled out of selection for the game against South Africa," the Irish Rugby Football Union said in a statement.
"His calf strain has been slower to heal than expected.
"He is partaking in modified training, but a decision has been made not to risk him this weekend, and his progress will continue to be monitored."
