Olympique Lyonnais accused West Ham United on Friday of showing a "profound lack of respect" after Algerian forward Said Benrahma's proposed transfer to the French club collapsed.
Lyon said the English club did not attempt to carry out the steps needed on world soccer governing body Fifa's transfer matching system for the deal to go through on Thursday before the end of the January transfer window.
"Following this incomprehensible behaviour... the international transfer certificate could not be requested before closing time," Lyon said in a statement.
"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," it said.
"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 did not address Lyon's comments about why the transfer had failed, but confirmed in an email to Reuters that the deal was not completed in time.