The Ulster flanker has been ruled out of next Saturday's clash against South Africa in Dublin and the following week's appointment with Fiji at Thomond Park, Limerick.
Ferris, 27, suffered an ankle injury during Ulster's RaboDirect PRO12 victory over Edinburgh three days ago.
The Irish Rugby Football Union said no decision has yet been made on his availability for Ireland's autumn finale against Argentina on November 25.
Ferris' absence is the latest major injury blow for head coach Declan Kidney as Ireland prepare for their return to action after last summer's 3-0 Test series defeat in New Zealand.
Centre Brian O'Driscoll and hooker Rory Best have already been ruled out of the autumn games because of injuries, while lock Paul O'Connell has only taken a limited part in training.
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.