Lyon accused West Ham of “incomprehensible behaviour” and a “lack of respect” after the deal to take Said Benrahma to France collapsed late on Deadline Day.
Benrahma travelled to Lyon in a bid to complete the move before the French window closed at 10pm.
The deal was a loan with an obligation to buy – in total worth more than £15m.
However, despite Lyon claiming the deal was agreed, the move collapsed at the last minute with the Ligue 1 side blaming West Ham for the breakdown.
A statement released by the French club said: “Olympique Lyonnais were delighted to welcome Said Benrahma to Lyon this Thursday to finalize his transfer from West Ham. The two clubs had signed a temporary transfer agreement, and Olympique Lyonnais had obtained approval from the DNCG to allow the transfer to take place smoothly and transparently.
“However, at the start of the evening, while Olympique Lyonnais had entered all the administrative data on the dedicated FIFA platform (FIFA TMS), West Ham had never launched the slightest technical procedure on its part, despite the repeated reminders from the OL 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 profound lack of respect on the part of West Ham towards the institution and the player.
“The club reserves the right to initiate all appropriate procedures necessary to validate the transaction at a later date, and to hold West Ham responsible if necessary.”
West Ham responded with a statement of their own: “West Ham United can confirm that the Deadline Day deal for Said Benrahma to join Olympique Lyonnais was not concluded ahead of the deadline, with a deal unable to be completed before 11pm.”
Confusion surrounds Fornals deal to Real Betis
Real Betis claim a computer problem has scuppered their bid to sign Pablo Fornals from West Ham.
The Spain midfielder had agreed a £7m switch to the LaLiga club on deadline day, but the deal failed to go through.
Betis CEO Ramon Alarcon is hopeful the Fornals deal can still go through, however.
He told Spanish reporters: “There was a last-minute problem with Fornals, we think it was a computer problem.
“Betis sent all the documents correctly and on time and it seems West Ham had a computer problem. It wasn’t just with Betis it was with other deals. We hope that it gets resolved in the next few days.
“It was done on both sides. We imagine that with a computer error it can be resolved. We are working on it and we are optimistic.”
Fornals was at the London Stadium alongside his West Ham team-mates on Thursday, watching on as they drew 1-1 with Bournemouth.