Chelsea are under investigation for the third time in eight years over a potential breach of Fifa regulations on youth players.
The governing body confirmed on Tuesday it had launched an inquiry into the club’s conduct involving signing foreigners under the age of 18.
Chelsea overturned a transfer ban imposed in 2009 over their 2007 recruitment of Gaël Kakuta from Lens, while last year saw them investigated about Bertrand Traoré's move to Stamford Bridge after pictures emerged of the midfielder playing for them before he had international clearance.
A Fifa spokesman told the Daily Mail: “As the investigation is ongoing, no further comment is possible for the time being.”
Atlético Madrid are currently under a transfer embargo for breaching rules over the signing of minors, a decision that was upheld on appeal to the Court of Arbitration for Sport.
Real Madrid were also banned from recruiting players last year, with their punishment later reduced from two transfer windows to one.
READ MORE: Fresh Hazard to Real rumours emerge
READ MORE: Rio Ferdinand to become professional boxer
READ MORE: Man United asked to ban Lukaku song
Any potential breach of the rules by Chelsea was described as less serious than that by their Spanish rivals.
A club spokesman said: “Chelsea FC complies with all Fifa statutes and regulations when recruiting players.”
Liverpool and Manchester City have both been punished by the Premier League this year over the tapping-up of youth players.
The two clubs were fined and banned from signing academy prospects, with City sanctioned for contacting parents of players too early in the recruitment process.
Liverpool, meanwhile, were found to have offered prohibited inducements to a Stoke City schoolboy and his family.
That was after Telegraph Sport exclusively revealed the club were under investigation, with the family of the boy left thousands of pounds in debt in private school fees and him unable to join another academy until Stoke were paid £49,000 in compensation.