Liverpool could face punishment for fielding an ineligible player in its third-round win over MK Dons in the English League Cup.
Liverpool says the club is aware of a "potential administrative issue pertaining to one of our players" and is "working with the relevant authorities in order to establish the facts of the matter."
The identity of the player has not been disclosed.
The story was first reported by The Athletic on Saturday.
Liverpool could be fined or, at worst, be thrown out of the competition.
Liverpool manager Jurgen Klopp fielded a young team in its 2-0 victory on Tuesday. It set up a fourth-round match at home to Arsenal.