O'Connell and Ferris have lost their battles with respective back and ankle injuries, ruling them out of the climax to the Guinness Series on Saturday week.
The Lions forwards' absence means Ireland will be without six key personnel against the Pumas, with Brian O'Driscoll, Rory Best, Rob Kearney and Sean O'Brien completing the list.
It is yet further bad news for Ireland, who were edged out 16-12 by South Africa on Saturday despite leading 12-3 at half-time.
Fiji are the next assignment - in a non-cap international at Thomond Park - but all eyes are trained on Ireland's meeting with Argentina, with defeat potentially dropping them into the third tier of seeds for the 2015 World Cup draw.
Ireland sank to eighth in the IRB's latest rankings, the gauge used to determine seedings for the 12 directly qualified teams for the tournament, which is being hosted by England.
For the Irish to plummet to ninth, results this weekend would have to go against them, with Scotland beating South Africa and Wales defeating Samoa.
Scrum-half Eoin Reddan, a substitute against the Springboks, will see a specialist this week after sustaining bruising to his ankle, so Ulster's Paul Marshall has been drafted into the squad.
Lock Donnacha Ryan and prop Cian Healy have passed mandatory concussion tests.
Gilbert has released a new line of rugby cleats. The Gilbert Virtuo 8S is part of the exciting new product. Check it out.
The entire All Blacks apparel line has been updated for 2013/14. Check out the New Zealand All Blacks polo.
The Nike Tiempo is a solid rugby cleat and one of few styles still made from full-grain natural leather.
The Gilbert Blitz 8S rugby cleat is a great cleat at a great price of $69.99. Get a new pair of cleats today.
A cool looking all black rugby cleat with the high performance adidas is known for. Get in the Gear!
Wear the crest of the British and Irish Lions on your t-shirt. A great look for the summer.
The All Blacks Performance t-shirt is black with hints of blue from the training jersey. Very Cool.
The New Zealand All Blacks training jersey for 2013/14. Get in the Gear!
The USA Rugby Pro Alternate rugby jersey is perfect for any fan of the Eagles. Get yours to wear during the summer Test matches.
The NEW All Blacks 2013/14 jersey has arrived at World Rugby Shop. Dare to wear the colors of the All Blacks.