Sexton blow to Ireland
The 30-year-old – who went off with the injury in the first-half of the 24-9 victory over France last Sunday – will be replaced in the starting XV by Ian Madigan, who performed well when he came on against the French.
Paddy Jackson, the third choice flyhalf, moves onto the replacements' bench while the Irish have also called up Isaac Boss as cover at scrumhalf, a position in which Madigan also plays.
"Post training yesterday [Friday] Johnny Sexton tightened up and although scans earlier in the week were normal, a further scan yesterday [Friday] afternoon revealed a very minor adductor strain," read a team statement.
"It was therefore felt that it was better to withdraw him from the game rather than risk further injury."
The New Zealand-born Boss, 35 and capped 23 times since making his Test debut in 2006, was originally left out of the squad because Ireland coach Joe Schmidt considered that Madigan was an able enough player at scrum-half to cover there.
However, they have decided they have enough cover for the centre position left vacant by the tournament-ending foot injury to Jared Payne to not call up the likes of last year's player of the year Andrew Trimble.
"With Ian Madigan now starting tomorrow's match versus Argentina it's ideal for him to focus fully on the out-half position," said the statement.
"The centre position vacated by Jared is well covered by Robbie Henshaw, Keith Earls, Darren Cave and Luke Fitzgerald."
Ireland – revised: 15 Rob Kearney, 14 Tommy Bowe, 13 Keith Earls, 12 Robbie Henshaw, 11 Dave Kearney, 10 Ian Madigan, 9 Conor Murray; 8 Jamie Heaslip (captain), 7 Chris Henry, 6 Jordi Murphy, 5 Iain Henderson, 4 Devin Toner, 3 Mike Ross, 2 Rory Best, 1 Cian Healy.
Replacements: 16 Richardt Strauss, 17 Jack McGrath, 18 Nathan White, 19 Donnacha Ryan, 20 Rhys Ruddock, 21 Eoin Reddan, 22 Paddy Jackson, 23 Luke Fitzgerald.
Date: Sunday, October 18
Venue: Millennium Stadium, Cardiff
Kick-off: 13.00 (12.00 GMT, 09.00 Argentina Time)
Referee: Jérôme Garcès (France)
Assistant referees: Romain Poite (France), Chris Pollock (New Zealand)
TMO: George Ayoub (Australia)
Agence France-Presse
