The Football League in England is investigating Liverpool to find out if the English Premier League club potentially fielded an ineligible player against MK Dons on Wednesday.
Liverpool had beaten League One side MK Dons 2-0 in the third round of the League Cup.
Possible sanctions could include a fine or Liverpool being removed from the competition.
The identity of the player in question was not disclosed.
“We are currently considering the matter,” an EFL spokesman said.
Liverpool beat the third-tier side to set up a fourth round clash with Arsenal.
Manager Jurgen Klopp fielded four teenagers in the starting line-up for the third round clash.
“The club are aware of a potential administrative issue pertaining to one of our players,” a Liverpool spokesman said.
“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.”