Manchester United were defeated on spot kicks by League Two outfit Grimsby Town last week.
Ruben Amorim's side bowed out of the Carabao Cup at the Second Round having lost 12-11 on penalties to fourth tier Grimsby.
David Artell's side went two goals up at Blundell Park but were pegged back by their Premier League opponents, sending the tie straight to a shootout, per competition rules.
Grimsby Town fielded ineligible player in Manchester United cup win
A statement from the EFL on Tuesday, September 2 confirmed Grimsby have been sanctioned for fielding an ineligible player during the match.
The Mariners' Clarke Oduor was registered at 12:01pm on the day before the fixture, one minute after the registration deadline had passed.
Grimsby self-reported the transgression following their fixture and have subsequently been penalised by the EFL.
Artell's outfit have been fined £20,000 - half of which is suspended until the end of the 2025-26 season - for their rule breach.
Man United will not be readmitted to the competition, nor will they take Grimsby's place in the Third Round.
Grimsby visit Sheffield Wednesday in the next round of the cup, who themselves defeated Premier League opponents Leeds United in Round Two.
A section of the EFL statement, relating to the club's punishment read: "Following a comprehensive review of all the evidence and considering prior decisions taken in respect of offences in the League Cup, the Board determined that the issuing of a fine followed precedent.
"The Board further noted the Club’s non-compliance was not deliberate with no intention to deceive or mislead. The Club has since implemented several actions to prevent a similar occurrence in the future."
