Said Benrahma's deal to join Lyon dramatically broke down on deadline day, with the French club releasing an explosive statement in which they accused West Ham of 'incomprehensible behaviour'.
Benrahma completed his medical in France on deadline day but Lyon have accused the Premier League club of failing to file the paperwork required despite continuous reminders, adding that they have shown 'a deep lack of respect' towards them and the player.
It is understood West Ham are unhappy with the reaction, feeling they simply ran out of time after negotiations proved difficult throughout the day with Benrahma's representatives.
Lyon plan to appeal in a bid to make sure the transfer goes through, as they said in their statement: 'In the early evening, when Olympique Lyonnais had entered all the administrative data on FIFA's dedicated platform (FIFA TMS), West Ham had never launched any technical procedure on its part, despite OL's repeated reminders and continuous mutual telephone communication.
'In the absence of this reciprocal action on the part of the English club and following this incomprehensible behaviour, raising questions, the international transfer certificate could not be requested before closing time.
'Olympique Lyonnais deeply regrets this situation and this decision, demonstrating a deep lack of respect on the part of West Ham for the institution and the player.
'The club reserves the right to initiate all appropriate procedures necessary to validate the operation later, and to hold West Ham accountable if necessary.'
West Ham struggled to a 1-1 draw with Bournemouth on deadline day as manager David Moyes bemoaned their lack of a left-sided winger.
Benrahma had agreed to join Lyon on loan with a £15million clause inserted. As of last night, not even senior sources at West Ham knew if Pablo Fornals's move to Real Betis had gone through in time.