Italian club Fiorentina are considering a formal complaint to FIFA over the signing of teenage defender Michele Fornasier by Manchester United.
The club have made initial contact with FIFA but no investigation has yet been launched.
United are confident of their legal position - players aged under 18 are not legally permitted to sign contracts in Italy and Fornasier was not contracted to Fiorentina when he was signed by the Manchester club this year.
Fiorentina are furious at losing out on the 16-year-old, however, and have written to FIFA.
A FIFA spokesman said: "FIFA can confirm that we were contacted by Fiorentina with regard to the potential transfer of the player, Michele Fornasier, to Manchester United.
"However, so far no formal investigation was opened since the relevant documentation still needs to be completed. Only then will we be in a position to evaluate possible future steps to be taken."
Fornasier is not the first Italian teenager signed by United - striker Federico Macheda joined from Lazio when he was 16, and another defender, Alberto Massacci, joined from Empoli this summer.
Empoli have not complained but United have asked the FA to seek international clearance from FIFA for Massacci as none has been forthcoming from the Italian FA.
The FIFA spokesman added: "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."