FIFA are investigating Premier League champions Chelsea for the third time in eight years over a potential breach of young player regulations.
"We can confirm that an investigation is ongoing," FIFA said in an emailed response on Wednesday to questions about media reports regarding the club signing foreign players under the age of 18.
"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.
A Chelsea spokesman said that the club complies with all FIFA statutes and regulations when recruiting players.
The Daily Mail newspaper said the alleged breaches were less serious than those committed by Spanish sides Atletico and Real Madrid in recent years, who both incurred transfer bans.
Chelsea have been investigated twice previously over their signing of minors.
The West London club were banned from signing players for two transfer windows in 2009, a penalty they had overturned on appeal in 2010, over Gael Kakuta's 2007 move from Lens to Stamford Bridge.
They were also investigated over the transfer of Bertrand Traore, the Burkina Faso international who was signed after his 18th birthday but had appeared in an under-18 match in 2011 while still 16.