Arguably their best lineout proponent as well as a vital cog in the engine room, the loss is expounded by the fact that pack (and team as a whole) always tend to play better when he is on the park.
Kane Douglas will replace Horwill in the starting lineup, which bring Ben McCalman onto the bench to cover the second row.
In his absence Will Genia will lead the side (Genia lead the team when they beat the Springboks in Perth last year).
‘Will is a proven leader and has had plenty of success as captain for the Reds and also for Australia,’ said Wallaby coach Ewen McKenzie. ‘He is a player who thrives with the added responsibility and he has always stepped up when given the opportunity to lead. I’m sure this will bring the best out of him.
‘It’s extremely disappointing to lose James but after discussions with medical staff we felt it was important not to risk further injury when he isn’t ready. Scans revealed his injury was on the lower-end in terms of severity and we expect him to be back to full fitness when we embark on our two-game tour of South Africa and Argentina in a few weeks.’
Wallabies (revised) – 15 Israel Folau, 14 Nick Cummins, 13 Adam-Ashley Cooper, 12 Christian Leali’ifano, 11 James O’Connor, 10 Quade Cooper, 9 Will Genia (c), 8 Ben Mowen, 7 Michael Hooper, 6 Scott Fardy, 5 Kane Douglas, 4 Rob Simmons, 3 Sekope Kepu, 2 Stephen Moore, 1 James Slipper.
Subs: 16 Saia Faingaa, 17 Scott Sio, 18 Ben Alexander, 19 Ben McCalman, 20 Jake Schatz, 21 Nic White, 22 Matt Toomua, 23 Jesse Mogg.