Grimsby Town fielded an ineligible player against Manchester United in the second round of the Carabao Cup last month, according to the Daily Mail journalist Mike Keegan.
The Red Devils were dumped out of the competition by the League Two club after losing to them on penalties following a 2-2 draw.
It has emerged that the registration of Clarke Odour was posted at 12:01pm a day before the game – with 12pm being the deadline.
Grimsby has been fined £20,000 (with £10,000 suspended), but they should have been thrown out and Man United could look to react to the development.
The Red Devils could insist on a replay if the League Two club are not thrown out, but the rules have been broken and a fine is not enough.
Man United found themselves 2-0 down after 45 minutes against the minnows before late goals from Bryan Mbeumo and Harry Maguire helped them draw level.
Grimsby won 12-11 on penalties and are due to face Championship club Sheffield Wednesday in the third round of the competition later this month.
It will be intriguing to see what happens but Man United could do with a second chance in the competition given that they are not playing in Europe this term.
The EFL Board, acting as the Management Committee of the Carabao Cup, claimed they have decided to fine Grimsby following a comprehensive review of all the evidence and considering prior decisions taken in respect of offences in the competition.
The Board determined that the issuing of a fine followed precedent and they further noted that the non-compliance was not deliberate with no intention to deceive or mislead.
Man United goalkeeper Andre Onana had a game to forget against the Mariners, which has forced the club to sign Belgian goalie Senne Lammens from Royal Antwerp.
