Attwood, who will join Bath from Gloucester ahead of the new Premiership season, suffered the injury in the Saxons' impressive 41-14 win over Tonga at Kingsholm on Sunday.
Sale back-rower Carl Fearns has been called into the squad as a replacement, with his Sharks club-mate James Gaskell set to provide second-row cover.
An RFU statement read: "Carl Fearns has been called into the England Saxons squad as an injury replacement for Dave Attwood ahead of this weekend's Churchill Cup final against Canada.
"Lock Attwood has been ruled out of the game by a right knee injury sustained in the Saxons' 41-14 win against Tonga on Sunday and is due to see a specialist tonight."
The Saxons had already lost captain Luke Narraway to a back injury after the Gloucester number eight complained of soreness before the tournament opener against the USA.
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.