The Irish squad have arrived in Queensland ahead of their three-test tour against Australia but captain Rory Best was not among the players.
A hamstring injury has sidelined the Ulster-man and Munster's Niall Scannell will replace the British and Irish Lions hooker in Ireland's squad.
Head coach Joe Schmidt explained that vice captains Johnny Sexton and Peter O'Mahony could share the captaincy for June's three-Test series against the Wallabies.
Before boarding the plane to Australia, boss Schmidt explained how his squad may handle the 35-year-old's absence.
"Rory's not going to tour," said Schmidt.
"He had a hamstring issue that kept him out of the game against Ospreys and we felt he was really going in the right direction and he would be ready for game one, definitely for game two. But he's just not quite where we need him to be.
"Because a number of these things have just become apparent, we've two vice captains in Peter O'Mahony and Johnny Sexton and a strong leadership group.
"It will depend a bit on selection and what we feel we need at any given time.
"It could be that Pete and Johnny take the team on and share the load."
Best picked up his hamstring concern in the build-up to Ulster's Champions Cup play-off with Ospreys, missing the Ravenhill province's 35-17 win on May 20.
Now the evergreen front-rower has failed to recover in time for Ireland's tour, leaving Leinster's Sean Cronin heading the queue to to start the first Test, in Brisbane next weekend.
Rob Herring is the other hooker in Ireland's touring party, with Schmidt now to decide who will skipper the team.
Schmidt's initial installation of Best as captain for the summer tour had pushed the Ulster star one step closer towards skippering Ireland at the 2019 World Cup.