Grimsby have been fined by the EFL for fielding an ineligible player in their shock Carabao Cup victory over Manchester United last week.
The Mariners beat United 12-11 in a penalty shoot-out, having led 2-0 in normal time before being pegged back.
The EFL said the breach related to Clarke Oduor, who came on as a 73rd-minute substitute.
The player's registration was submitted at 12.01pm on the day before the match, shortly after the 12pm deadline required in accordance with this season's competition rules.
The League Two club have been fined £20,000, with £10,000 suspended until the end of the season which would be triggered if they fielded an ineligible player in any EFL competition.
The EFL said Grimsby self-reported the breach once they discovered the error the day after the match.
The EFL said the issuing of a fine followed precedent following a comprehensive review of all the evidence and considering prior decisions in respect of offences in the League Cup.
The EFL's board determined the club's non-compliance was not deliberate, with no intention to deceive or mislead.
In 2023, Barnsley were kicked out of the FA Cup after fielding an ineligible player in a first-round replay against Horsham.
Manchester United did not wish to comment when contacted but it is understood the club will not seek a return to the competition.
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