Paul O'Connell's Ireland career ended as he suffered a serious hamstring injury in last weekend's win over France

World Cup quarter-final: Ireland v Argentina Venue: Millennium Stadium, Cardiff Date: Sunday 18 October Kick-off: 13:00 BST Coverage: Live on BBC Radio 5 live and BBC Radio Ulster, plus live text commentary on BBC website

Ireland will miss Paul O'Connell's inspirational presence and leadership on the pitch against Argentina on Sunday but I still think he will play a major role in helping his country reach the World Cup semi-finals.

From what we are being told, he will be rejoining the squad before Sunday's quarter-final following his hamstring surgery and I can guarantee you that he will be delivering the mother of all rallying speeches to the players before the game.

By all accounts, Paulie's selflessness was exhibited in the Ireland dressing-room after last weekend's magnificent win over France.

Many of us would have been down in the dumps in those moments after suffering an injury which you knew was the end of your international career as well as dashing cherished dreams of playing in a World Cup final.

But that's not Paul O'Connell's way.

I've heard from a few of the boys that he was really upbeat in the dressing room and talking about the pride he felt in his team-mates. That's just so typical of the man.

Ireland face tough task against in-form Pumas

With Ireland's talisman missing and other strong characters like Johnny Sexton, Peter O'Mahony and Sean O'Brien also ruled out, that might lead to concerns about a leadership deficit but I expect new captain Jamie Heaslip and Rory Best to fill that void by taking on increased responsibility on Sunday.

Best was at the absolute top of his game last weekend.

There was one passage of play in the second half where Rory made tackles four or five times in a row - in between sticking his head in the ruck trying to steal the ball several times.

It was one of most remarkable bits of action I've seen on a rugby field.

Overall, the key for Ireland on Sunday will be avoiding early mishaps.

If Argentina do go six or 10 points up then a few doubts could creep into Ireland ranks - given the big names that are missing.

Even during Joe Schmidt's reign, Ireland have sometimes struggled when chasing games and you don't want to have to get into that position against a team with backs of the quality of Nicolas Sanchez, Juan Martin Hernandez and Juan Imhoff.

It is going to be an extremely tough test against an Argentina line-up whose attacking ability is far superior to that of the Pumas squad that reached the World Cup semi-final in 2007 - when they beat Ireland along the way.

The old stager Juan Martin Fernandez Lobbe, Argentina's talisman in the O'Connell or Sergio Parisse mould, remains from that squad.

During my career, Lobbe and I ran over each other a few times and he is a player I have lot of respect for.

Lobbe's presence is another reason why I would have opted to switch Iain Henderson to the back row because the young Ulsterman is capable of producing the kind of astonishing physical intensity which O'Brien delivered last weekend.

Stephen Ferris says he would have opted to play Iain Henderson in the back row in place of Sean O'Brien

Schmidt has decided otherwise with Jordi Murphy named at six and in fairness to the coach, he hasn't got too many big selection calls wrong during his Ireland reign.

However, you have to think that O'Brien - on last weekend's form - is going to be missed and you just hope that it won't be the deciding of the game.

With Sexton ruled out, his replacement Ian Madigan should be full of belief after his brilliant contribution last weekend.

Perhaps even more importantly, Ian's team-mates will also have full confidence in him.

Ireland won't make same mistake as 2011

Win or lose on Sunday, I don't think Ireland will mentally throw it away in the fashion that we did, alas, at the World Cup four years ago.

That was in the quarter-final against Wales which was the ultimate deflation after the high of our pool victory over Australia.

Schmidt is so meticulous and he will be fully aware of what happened in 2011 and will have taken measures to ensure there isn't a repeat.

Looking back, I think we stepped over that thin enough line between supreme confidence and complacency.

We were so convinced we were going to win after looking far more impressive than Wales during the pool stages.

Stephen Ferris and Paul O'Connell were in the Ireland team surprised by Wales in the 2011 World Cup quarter-final

There was talk about Ireland having the best back row in the world and we just started to believe all that and already had half an eye on a seemingly winnable World Cup semi-final against England or France.

Schmidt's Ireland never, ever get ahead of themselves. He just totally forbids that.

Despite all the injuries and O'Brien's suspension, Ireland will be ready to deliver the optimum performance and whether that will be good enough to see off the Pumas is the big question.

Sunday's game is likely to be a lot tougher and closer than the France match, but I believe Ireland will edge a tight verdict and reach the country's first ever World Cup semi-final.

Stephen Ferris was talking to BBC Sport's John Haughey