Mexes turned down a move to United and agreed a four-year deal with Roma instead, however, his club Auxerre are demanding that if Roma want to sign the player then they should pay the fee offered by United.
According to BBCi, Mexes contacted Fifa to ensure his move would go through only for the case to be passed on to France's equivalent of the F.A. - the French football Federation.
His case will now go before a sports arbitration panel, which, should it go unfavourably for the defender, will put Mexes back on the transfer market.