An investigation into Chelsea's recruitment of youth players has been launched, Fifa has revealed.
The Premier League champions were subject to sanctions from the world governing body previously concerning Gael Kakuta's transfer from Lens in 2007, which were subsequently appealed successfuly to the Court of Arbitration for Sport (CAS).
"We can confirm that an investigation is ongoing, however please note that we cannot provide any details concerning the matters under investigation. We have no further comment," a Fifa statement said.
Burkina Faso international Bertrand Traore played for Chelsea's under-18s side when aged 16, which was an apparent breach of Fifa regulations.
Traore could not establish himself as part of the senior Chelsea set-up and had loans spell in Holland with both Vitesse Arnhem and Ajax before earlier this summer completing a permanent move to French club Lyon.
If eventually found guilty of wrongdoing, there is the possibility Chelsea could face the prospect of being placed under a transfer embargo.
In 2016, Fifa ruled Spanish club Atletico Madrid would be banned from registering players across two transfer windows for breaching rules over the signing of minors under 18 - a decision which was upheld by CAS on appeal.
Chelsea maintain the club complies will all the Fifa regulations when recruiting players.
Chelsea believe Traore was the subject of an "option agreement" which allowed him to play in friendly games.
The west London club said at the time: ''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.''
The Premier League said all rules were followed in Chelsea's signing of Traore on January 1, 2014, the first day of the transfer window opening following his 18th birthday, on September 6, 2013.
What raised questions was the earlier recruitment of Traore and his participation in a Chelsea under-18s match at Arsenal on October 23, 2011, when he was 16.
The report on Arsenal's official website mentions Traore brushing the top of the crossbar with a 30-yard shot in the friendly fixture where his Chelsea team-mates included goalkeeper Jamal Blackman and midfielder Ruben Loftus-Cheek, who went on to be part of Chelsea's first-team squad.
International transfers are only permitted for players over the age of 18 - unless the player in question meets one of three qualifying criteria.
Under-18s can move to a club in a different country if their parents move there for non-footballing reasons, if they are from another nation within the European Union or European Economic Area and aged between 16 and 18, or if they live within 100km of the club.
Traore came to notice when he travelled from his home in Bobo-Dioulasso to Ouagadougou and immediately impressed coach Rainer Willfeld, according to Fifa.com.
He was included in the Burkina Faso squad for the 2009 Fifa Under-17s World Cup where he was the tournament's youngest player at the age of 14. Despite this, his ability shone.
There were a number of clubs interested in signing the teenager but Burkina Faso sports minister Jean-Pierre Palm announced in August 2010 that Traore - one month prior to his 15th birthday - would sign for Chelsea.
He attended the fee-paying Whitgift School in Croydon, south London, but did not play in school competitions.
Traore became Whitgift's first full football international, with Victor Moses following when he represented Nigeria.
It was as a trialist on Chelsea's pre-season tour to Asia in 2013 - the first of Jose Mourinho's second spell as manager - when there was even more interest in his ability and he scored against a Malaysia XI in Kuala Lumpur.
Mourinho said then: ''Now we want to keep him. We have to wait until he becomes 18 to try to get a permit for him to stay in England.
''It's the rules and we have to accept them. He plays for his national team. Sooner or later the committee has to give him a permit to play in England.''
Chelsea acted decisively before a change in Football Association regulations to obtain a work permit for Traore, who travelled on the July 2015 tour to North America.