Le Havre insists United broke transfer rules when they signed 16-year-old Paul Pogba.
United has hit back and has urged Le Havre to retract their comments.
“It is corruption of a young player, he was under contract,” Le Havre chairman Jean-Pierre Louvel told L’Equipe.
“Threats won’t make us step back. Our lawyers will submit the case to Fifa, we will go until CAS (Court of Arbitration for Sport) if needed.
“Pogba had to sign a trainee contract, but he didn’t do it, and his parents didn’t want to.
“Now he has no licence to play at Manchester, and FFF (French Football Federation) didn’t give him a letter of release, which means there is a problem.
“The big clubs can’t act that way. The player has been lost, but we expect sanctions to protect our education.”
