Barcelona are currently banned from registering players after they were handed the same ban for similar reasons a year ago.
The Catalan giants unsuccessfully appealed that ruling to the Court of Arbitration for Sport (CAS), however, the appeal did delay the application of the ban until January which allowed them to sign seven players, including Luis Suarez last summer.
The same route of appeal would be open to both last season's Champions League finalists.
"We are not in a position to comment on any proceedings that are ongoing.
No further information can be provided for the time-being," said a FIFA spokesperson when contacted by AFP on Wednesday.
Real Madrid confirmed in January that FIFA had asked for information pertaining to 51 players in their youth system.
Cadena SER also reported that Madrid's unusually busy January transfer window had been carried out with one eye on a possible ban.
The European champions signed Norwegian prodigy Martin Odegaard, 19-year-old Marco Asensio from Mallorca and Brazilian under-21 international Lucas Silva in January.
Moreover, the club have announced that Porto right-back Danilo will join Madrid in the summer for a fee of 31.5 million euros ($34.2 million, £23 million).
Under FIFA rules the signing of foreign players under the age of 18 is not permitted apart from in three exceptions.
Firstly, that the parents of the player relocate to the country for non-football reasons, that the player is aged between 16 and 18 and the transfer takes place within the European Union or European Economic Area, or that the player lives no further than 100 kilometres from the club's headquarters.