The Toffees lost 2-1 in the Merseyside derby clash to miss out on a place in the final, and the 25-year-old was a notable omission from David Moyes' selection for the game.
An Everton spokesman confirmed: "Royston Drenthe has been the subject of a disciplinary matter. This has been dealt with internally and the club will be making no further comment."
Netherlands international Drenthe has scored four goals and provided seven assists since joining the club on loan from Real Madrid in the summer.


