FIFA's general secretary Jerome Valcke has revealed that an investigation into 15 English transfers could take years to complete - but that none are as serious as the case which led to a transfer ban on Chelsea.
Valcke said FIFA were inundated with complaints the day after the disciplinary action against Chelsea was announced.
The club were found guilty of inducing the French teenager to break his contract with Lens in 2007 when he was 16 and banned from making signings for two transfer windows. The club are appealing.
FIFA are now looking into 15 other cases from England, involving Manchester United and Manchester City among others.
Valcke, speaking in the USA, said: "The day after [Chelsea] we received a number of letters and calls. We have 15 investigations in England and we know already that these investigations are not at the same level as the Chelsea one.
"Everyone is coming with lawyers, and then it takes years, at least months, to finalise cases."
Under new rules which coming into force next month, a FIFA sub-committee will have to approve all international transfers of players aged under 18.