Mitchell dislocated his ankle and broke a bone in his leg after he collided with Scott Higginbotham of the Reds during their match on Saturday, 23 April and was initially ruled out of the 2011 Rugby World Cup. However, he subsequently made a full recovery and was included in Australia's tournament squad. He made one substitute appearance against Ireland and in two starts scored one try against the USA and two against Russia. He injured his hamstring in the final pool stage match of the 2011 World Cup, and missed the remainder of the tournament. In the lead up to the 2012 Super Rugby season Mitchell suffered an ankle problem, and missed the Waratahs pre-season games. He did not play any games in the first half of the competition, making only five appearances all season.