His hamstring injury forced Cooper to withdraw from the starting line-up for the 2006 State of Origin series, being replaced by winger Eric Grothe, Jr. from the Parramatta Eels. After missing the first game of Origin for New South Wales, Cooper failed to be called up for game two with Grothe retaining his position after a solid performance in game one. On 11 June it was announced that Cooper had been called up as 18th man on stand by for the game.
Due to a hamstring injury, Cooper was forced to sit out the starting lineup for the 2006 State of Origin series and was replaced by Eric Grothe, Jr. from the Parramatta Eels. After missing the first game for New South Wales, Cooper did not get called up for the second game, with Grothe retaining his spot after a strong showing in the first game. On June 11, it was revealed that Cooper had been brought into the team as an 18th man on standby for the game.