The 27-year-old had only returned to full fitness in time for the tournament after he dislocated his ankle in April.
And he looked to be close to his best form as he crossed for a try against the USA and then for two in the win over Russia.
However it was it the process of breaking away for what would have been his hat-trick try against the Bears that Mitchell pulled up sharply, grabbing his left hamstring.
A subsequent scan has shown that Mitchell suffered a grade one tear, meaning he faces around six weeks out.
Mitchell joins No.8 Wycliff Palu is leaving the Wallabies squad, with Matt Hodgson and Lachie Turner now confirmed as their replacements.
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.
$29.99
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.
