As David Gill, the United chief executive, reiterated the club's outrage over Le Havre's claims that they stole Paul Pogba and the midfield player's parents prepared to sue the French club for libel, the champions faced fresh scrutiny over their transfer policy. Fiorentina are still compiling their submission to Fifa, although the details of the Italian club's apparent complaint are unclear at this stage.
The rules governing Italian football prevent their clubs from tying players under the age of 18 to a contract, a situation that United are understood to have exploited to sign Fornasier and, two years earlier, Federico Macheda, the striker, from Lazio. Fornasier, who turned 16 last month, represented United's academy team at the Northern Ireland Milk Cup in July.
Fifa said in a statement: "We can confirm that we were contacted by Fiorentina with regard to the potential transfer of the player, Michele Fornasier, to the English club, Manchester United. However, so far no formal investigation was opened since the relevant documentation needs to be completed." United's capture of Alberto Massacci, another young Italian defender signed from Empoli this summer, is also being investigated by Fifa.
A spokesman for the world governing body said: "We can confirm that our services were contacted by the Football Association on behalf of its member club, Manchester United, with regard to the international clearance for the player Alberto Massacci since the FA was not able to receive the pertinent international transfer certificate from the Italian Football Federation (the association of the player's former club). We are currently investigating the matter."
The news came as Gill launched a staunch defence of United's recruitment policy after Le Havre's claims over Pogba fuelled fears that the club could face a transfer ban similar to that imposed by Fifa on Chelsea for inducing Gaël Kakuta to break his contract with Lens.
"We will not accept the good name of Manchester United being trawled around on websites and the press to say that we have done things which we are not allowed to do and we would never do. We've done everything, we think, by the book. We are not intimidating Le Havre [by threatening legal action]. We have no intention of intimidating Le Havre."
Fifa is still awaiting Le Havre's formal complaint but Gill claims that United are unconcerned. "They can do whatever they feel is appropriate," he said. "We can defend our case in the football bodies. We are very comfortable doing that."
Gaël Mahé, Pogba's agent, also claimed that no wrongdoing had taken place. He said: "No money had changed hands up front, though Paul will get a very good contract when he turns professional. All he has from United is a flat in Manchester for him and his mother to live in. The problem is that there are three things Le Havre do not have. They do not have a contract aspirant, they do not have convention of formation and they do not have a late-trigger contract. All they have is a contract of non-solicitation, which is invalid outside France.
"We spent a long time ensuring that the document we signed with Manchester United was legally watertight."