The EFL is looking into whether Liverpool fielded an ineligible player during their game against MK Dons in the Carabao Cup on Wednesday.
Jurgen Klopp made 11 changes ahead of the 2-0 win, at Stadium MK, handing debuts to Caoimhin Kelleher, Rhian Brewster, Herbie Kane, and Harvey Elliott.
Sepp van den Berg, who signed from Dutch club PEC Zwolle in the summer, made his first start for the Reds off the bench.
But it was the appearance for Spanish midfielder Pedro Chirivella who is believed to be the player ineligible that has sparked the controversy.
Liverpool have admitted that there is a "potential administrative error pertaining to one of our players".
A club statement adds: "We are working with the relevant authorities in order to establish the facts of the matter and will be making no further comment until this process is complete."
Back in 1999 West Ham were ordered to replay their League Cup quarter-final against Aston Villa after an administrative error meant Emmanuel Omoyinmi was ineligible.
West Ham won the game at Upton Park to advance to the semi-finals but were made to replay the match which they duly lost.
However, in 2014 Sunderland fielded an ineligible player - due to an administrative error - for a cup game and a number of league matches but were only fined.
It is not yet known what, if any, action the EFL will take.
More on this as we get it.