Think the main concern is injuries and suspensions in the defence. When you think about it would take 3 injuries/suspensions till we were really struggling. Miller can cover full back and centre back. Hall centre back. A third injury/suspension would mean someone like Todd or Telfer for example having to cover full back. I know that prospect sounds scary but they are ment to be professional footballers.
This would obviously weaken the team but still not that bad. An injury/suspension to McManus would be worse in my opinion