ok it can take days before the full effects, but we're talking about minutes. Top end footballers are very good at writhing around to highlight fouls- yet Karius just got up. He complained for sure but he obviously didn't regard what happened as needing professional attention, nor did the ref who has pretty clear instructions about head injuries. So at the time it was considered minor by all concerned.
Subsequently, Karius turns up in Boston on a family holiday and is then (and only then) sent to see a doctor for a diagnosis, where he's found to have concussion. Much of the diagnosis is based on "
carefully reviewing game film". The doctors were Dr Ross Zafonte, of Spaulding hospital, where he just happens to be heavily involved in a
prestige project sponsored by the Red Sox, owned by Fenway who just happen to own Liverpool, together with Dr. Lenore Herget who is a
consultant to the Red Sox.
Karius only cost 5 million quid, which is peanuts in the footballing world but his owners have to think about the resale value.
Sorry for being a bit cynical.