Quite frankly Ryan and and lesser extent Brockman has surpassed Petch.Petch takes part in about 3 centre bounces even with the main trio (Yeo/Kelly/Reid) present.
With him out, it's likely those centre bounces will go to one of Flyin' and/or Brockman, who played pretty well there against Essendon last week.
Unlucky for the injury but if Ryan/Brockman are better in the mid then Petch I don't see a spot for Petch unless he reinvents himself up forward.
Seriously what has Petch got over Ryan in the mid? Only speed and endurance but for speed Ryan is no slouch and endurance not yet verified