The Federation of International Football Association (FIFA) are investigating Chelsea over a potential breach of young player regulations.
According to Sky Sports, FIFA responded on Wednesday to questions about media reports regarding Chelsea signing foreign players under the age of 18.
“We can confirm that an investigation is ongoing.” FIFA said in an email.
“We cannot provide any details concerning the matters under investigation.”
FIFA rules prohibit the international transfer of players under the age of 18 unless their parents have emigrated for reasons not connected to football or both the player and club are based within 50 kilometres of a national border.
The only other exception is for transfers within either the European Union or European Economic Area (EEA), where the minimum age is 16.
In those cases, clubs must still ensure that the player continues his education and studies for an alternative career, as well as making sure he has a high living standard.
This will be the third time in eight years that Chelsea will come under scrutiny over the transfer of young players.
In 2007 FIFA investigated Chelsea over transfer of Gael Kakuta from Lens and were banned from signing players for two transfer windows in 2009, a penalty they had overturned on appeal in 2010.
And in 2016, the Premier League champions were also investigated over the transfer of Burkina Faso international Bertrand Traore who was signed after his 18th birthday but had appeared in an under-18 match in 2011 while still 16.