Ireland back Robbie Henshaw has been ruled out of the tour of Argentina with a hand injury.
The 20-year-old was seen as favourite to succeed the retired Brian O'Driscoll but will have to sit out the two-Test series.
A statement from the Irish Rugby Football Union read: "Robbie sustained the
injury earlier in the season and it had not limited his ability to train or play.
"He exacerbated the injury in training this week and further specialist advice
has recommended that surgical repair of the damaged ligaments should not be
The Pumas are expected to provide a tough test for Ireland who are building towards the 2015 World Cup.
The great O'Driscoll retired from International rugby after Ireland beat France to clinch the Six Nations title in his 141st Test match.
And head coach Joe Schmidt may now select Ulster's Darren Cave to start in the midfield on 7 June in Resistencia.