Maybe still feeling effects from his concussion?

Could be he needs another week from his head knock - only a kid after all.

Possibly.  Coming back from a head knock to then play against a kamikaze pilot like Percival is not necessarily a great idea given his age and relative lack of experience.  I know he’d be able to handle it but possibly want to give him an extra week.  

Can he play prop?

Could be he needs another week from his head knock - only a kid after all.