Ireland shift focus to Pumas
O'Connell, capped 108 times by Ireland, is to undergo an operation on a hamstring injury sustained in the brutal 24-9 Pool D victory over France.
With a move to European heavyweights Toulon pending, it means the end to the 35-year-old stalwart's international career.
"Paul was a true leader and a true character off the pitch," said centre Robbie Henshaw.
"He was a truly inspirational leader. Each time he spoke he said the right thing.
"I loved and admired the fact that he was not always intense or worked up."
O'Connell's withdrawal follows those of flank Peter O'Mahony, who was ruled out after suffering knee ligament damage in the brutal victory over France, and first-choice centre Jared Payne [foot fracture].
There are still doubts over flyhalf Jonathan Sexton, who went off after 25 minutes of the France game with a groin injury.
"Paul O'Connell really was a true warrior," prop Jack McGrath said, adding the shaven-headed lock's forte was mastering the "minor details".
"Every time Paul's pulled on an Irish jersey over the last 15 years, he's never let it down.
"He hasn't left anything out on the pitch.
"Hopefully he'll be around for the next couple of days."
Like Henshaw, McGrath added: "It's a chance for other guys to step up."
Argentina went down 16-26 to defending champions New Zealand in their opening Pool C game but then went on to rack up the highest number of points in easily seeing off Georgia [54-9], Tonga [45-16] and Namibia [64-19].
Allied with their traditional forward strength based around an immovable front five and dynamic yet bruising back row, Nicolas Sanchez has ignited an exciting backline.
With wings Juan Imhoff and Santiago Cordero feeding off quick, go-forward ball and clever decision-making from scrumhalf Tomas Cubelli, Sanchez and play-making inside centre Juan Martin Hernandez, Los Pumas promise to be a handful come Sunday, according to McGrath.
"Argentina pride themselves on their physicality and we know we'll have to be ready," the prop said.
"We toured there two years ago and know them well.
"They pushed New Zealand in their first game so we can't take them lightly.
"They've got some great footballers and we're going to have do our homework."
Rhys Ruddock, called up as a replacement for O'Mahony, said the team had reacted well after seeing both the O'Mahony and O'Connell stretchered off in the France game.
"I'm sure the lads will know to fulfill what's expected of them and if Paul or someone goes off the field they need to step up and I think that's what we saw at the weekend," said Ruddock, the Irish-born son of former Wales coach Mike.
"In an 80-minute performance the team were outstanding last weekend.
"But in terms of intensity and physicality, this week will probably be at least the same level if not more."
Ruddock added: "Argentina have scored over 20 tries already in the tournament, they're looking to play rugby and they've got the footballers to do it now.
"They've come on a long way [from the game I played in 2014], they've also got some real quality backs as well."
Flank Chris Henry, who impressed when he came on against France, added that there would be extra motivation to perform for O'Connell and O'Mahony.
"We want to do it for those players, they've given so much not just in the last five weeks, but in the last decade," Henry said.
"It would be incredible to do something special for Paul and Pete."
Agence France-Presse
