Fagan is not expected to play again this year after suffering a broken tibia. Hull chairman Paul Duffen has promised to back Fagan, with legal action now possible.
"To be frank, this is the sort of incident that, had it happened in the street, would have been regarded as common assault," said Duffen. "I wouldn't want to prejudice any potential further action from Craig, yet what I will say is that he has the club's full support on this matter.
"The timing of it for Craig and the implications, short-term, for his career could be significant."