The letter West Ham sent to the Premier League proving Argentine forward Carlos Tevez was eligible to play for them has been seen by the BBC's Inside Sport.
The letter, which was sent on 27 April, stated the agreement between the club, the player and associated companies was "terminated with immediate effect".
Wigan chairman Dave Whelan had called for the documents to be made public.
He is concerned the Hammers have been breaking rules over third-party ownership during the season's finale.
Tevez scored the winner at Manchester United on the final day of the season which helped West Ham avoid relegation.
And the striker scored seven goals in the club's final 10 games of the season to help them claw their way to safety.
But recriminations over his move and the fact that West Ham were fined and not docked points over the signings of Tevez and his compatriot Javier Mascherano in August have marred their strong finish to the campaign.
Surely the contract can only be terminated by both parties?
Wigan chairman Dave Whelan
Whelan is aggrieved at the handling of the case and had called for "concrete evidence" that the termination was pushed through before 28 April, when his club played West Ham.
The letter seen by Inside Sport reads: "We hereby notify you that the private agreement (as so amended, varied, modified or replaced) is hereby terminated with immediate effect and shall cease to have any further force of effect."
Whelan had added: "Surely the contract can only be terminated by both parties?"
There appears to be some doubt over whether Kia Joorabchian, who part-owns one of the third party companies and played a key role in bringing Tevez and Mascherano to West Ham, agreed.
Wigan lost 3-0 to the Hammers with Tevez playing a key role in a victory which boosted their chances of survival and put the Latics further in jeopardy.
And that prompted an angry reponse from the Hammers' relegation rivals, who threatened legal action over the decision.
The Latics avoided the drop on the final day of the season with a win at Sheffield United which sent their hosts down.
But Whelan has promised to stand by the Blades, along with Fulham and Charlton, as he seeks "justice".
The Premier League says any action against the decision would be futile, because all 20 clubs agreed to the disciplinary system in place.