on GMTV Dr Hilary whotsit explained it is a cased of trying to monitor his brain to make sure it is not swelling - which would cause further damage - and in the meantime just waiting for it to sort itself out a bit from the original injury.
He also said complaining of lower back pain was a good sign - presumably it means the nerves are not damaged.
I guess it is like any brain damage - takes a long time before you know the full extent.
Time will tell. I hope he is lucky.