They are alleged to have breached FIFA regulations
Chelsea are potentially facing a ban on buying players as it has emerged they might have breached FIFA regulations on international transfers.
The Burkina Faso international Bertrand Traore played in an under-18s game for them at the age of 16 in October 2011, despite players needing to be over 18 to complete such a transfer.
Chelsea believed he was the subject of an agreement that allowed him to feature in friendly matches.
In a statement to the Press Association, the club said: "Bertrand Traore was registered by Chelsea FC in January 2014 in compliance with FA and Premier League Rules. Prior to that date, he was party to an option agreement which enabled the club to acquire his registration in January 2014. The option agreement was registered with, and approved by, both The FA and the Premier League."
A FIFA spokesperson also said that they could not comment on individual cases.
Barcelona served a transfer ban during 2015 over a breach of rules on the transfer of underage players, while their La Liga rivals Real Madrid and Atletico Madrid are appealing a similar ban.