Dublin - Ireland captain Rory Best has been ruled out of the tour of Australia with a hamstring injury, the Irish Rugby Football Union announced Thursday.
Munster's Niall Scannell will replace the Grand Slam winning skipper in the squad for the three-Test series against the Wallabies in June.
Johnny Sexton and Peter O'Mahony are set to share captaincy duties in the absence of the British and Irish Lions front row.
That the 35-year-old Best, capped 111 times, would not tour was confirmed by the IRFU on Twitter.
"With @RoryBest2 ruled out Joe (Schmidt) has said that @JohnnySexton & @peterom6 who are Vice Captains may share the captaincy in Australia #TeamOfUs."
Best was injured during the build-up to Ulster's Champions Cup play-off with Ospreys, missing the province's 35-17 victory on May 20.
With Best out of action, Leinster's Sean Cronin is in line to start at hooker in the first Test at Brisbane on June 9.