City captured teenage defender Jeremy Helan back in February and Rennes officials have now reported the matter to world football's governing body, claiming Helan was bound to them through a pre-contract agreement.
Rennes have said that Helan signed a pre-contract agreement with them as a 13-year-old, which tied the player and club to a deal if the player represented France at junior level.
Rennes technical director Pierre Dreossi told The Independent: "For us it was strange to have no discussion from City."
Eastlands officials insist there was nothing illegal about the transfer but now face anxious wait to hear the findings of world football's governing body, who recently banned Chelsea from signing any players until January 2011.
Man City last week