Gillies appeared to stamp on Joe El Abd and could miss the rest of the season for the offence but will also face the possibility of internal action from Worcester.
"The disciplinary procedure will take its course and we obviously have the wherewithal to invoke our own disciplinary process," said Worcester director of rugby John Brain.
Defeat came courtesy of two David Lemi tries and another effort by Sam Cox, while Mark Tucker and Thinus Delport replied for Worcester.
It meant Worcester failed to ease their relegation worries.
