(CNN)Liverpool faces possible expulsion from the English League Cup for fielding an ineligible player in last Wednesday's 2-0 third round victory over MK Dons.
Reports have identified Spanish midfielder Pedro Chirivella, who came on as a second half substitute in the win, earning the European champion a high profile tie against Arsenal in the last 16 of the knockout tournament.
Chirivella, who was making his first appearance for Liverpool since May 2016, spent the second half of last season on loan at Spanish second division club Extremadura, which means he would have required new international clearance when he returned to his parent club in the summer.
Liverpool requested that in July but the process can only be completed with the Football Association's intervention and it is unclear if the necessary paperwork was in place.
The English Football League (EFL), which administers its cup competition, said it was "currently considering the matter," in a statement.
The EFL has a range of sanctions at its disposal, ranging from a fine to being thrown out of the competition.
Liverpool reacted to the reports by issuing its own statement.
"The club are aware of a potential administrative issue pertaining to one of our play