It is mentioned in the report that the situations surrounding the signings of both Gael Kakuta and Bertrand Traore prompted Federation Internationale de Football Association to investigate, and now they are doing so once again.
"The only other exception is for transfers within either the European Union or European Economic Area (EEA), where the minimum age is 16".
Chelsea have been investigated twice previously over their signing of minors.
This is the third investigation of this sort into the club's affairs in the last eight years.
They were also under investigation previous year over the signing of Burkina Faso forward Bertrand Traore after images emerged of him playing for Chelsea when he was just 16 and before he received global clearance.
Although it is not believed Chelsea's case is as serious as the two La Liga clubs, it will be up to Federation Internationale de Football Association what sanctions they bring when they have concluded their investigation.
Upon appeal that penalty was overturned, but the west London outfit were investigated once again a few years later over the transfer of Bertrand Traore after he signed a contract after his 18th birthday - despite appearing in an under-18's match at the age of 16.
The two clubs have been banned by the Premier League for two years from signing academy player due to tapping up.
Real Madrid have also been punished in the recent past and had their ban cut from two transfer windows to one. The decision was appealed, but upheld by the Court of Arbitration for Sport (CAS).
Both Liverpool and Manchester City are now banned by the Premier League from signing academy players after contacting parents too early in the recruitment process and offering prohibited inducements respectively. If found guilty then the Blues could incur another transfer ban.
Chelsea are adamant they comply with all the regulations when recruiting players.