Err.. what?
I am liable for my actions. If my actions cause harm, then I can be sued for that; either to reclaim costs (that's what insurance is for), or to be punitive (financially and professionally) if I am held to be negligent.
As far as I can tell, nothing in this situation is about the Dr, or any wrongdoing on his/her behalf. The Dr performed their duty, and diagnosed Cudmore as having concussion; the club (aka coach) then over-rules the Dr, and sent Cudmore back on the pitch.
Maybe the Dr could have fought his/her corner harder; but ultimately, unless he locked the door from the inside and barricaded the coach out, then there's not a lot more s/he could have done.
The medical difficulty comes in missing the diagnosis, giving inappropriate treatment, failure to warn about side-effects, or sods' law with unexpected or severe side-effects. None of these are at issue here (as far as I can tell)
ETA: OK, re-read the article, I'd obviously been lazy on my first reading - the Doc initially sends him to the showers; then comes back and asks him to go out on the field again - which is negligence and deserves to be sued for.