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 shootout, 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 12:01 p.m. on the day before the match, shortly after the 12 p.m. 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 another ineligible player in any EFL competition.
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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.