FIFA has reportedly accused Chelsea of breaking the rules on the signing of 25 foreign players under the age of 18.
According to The Guardian, the number of cases could rise, with the matter now in the hands of the world football governing body's disciplinary committee, which has the power to impose sanctions.
Chief among those sanctions is a ban on transfers, a fate suffered by La Liga trio Real Madrid, Barcelona and Atletico Madrid in recent years.
The three Spanish sides were investigated for infringements related to the signing of minors and each was given a two-window transfer ban, although Real served only one after a successful appeal to the Court of Arbitration for Sport (CAS).
FIFA confirmed last September that it was investigating alleged breaches at Chelsea of the recruitment of young players from overseas.
The case of Bertrand Traore reportedly alerted FIFA, the Burkina Faso forward signing professional terms as an 18-year-old in January 2014, but pictures are alleged to have emerged of the player involved in a non-competitive game against Arsenal in October 2011, aged 16.
The world governing body's rules prohibit international transfers for players under the age of 18, unless their parents emigrate for non-footballing reasons, the player and club are based within 50km of an international border, or the transfer is within the EU or European Economic Area, where the minimum age is 16.
A Chelsea spokesperson is quoted by Sky Sports News as saying: "Chelsea FC complies with all FIFA statutes and regulations when recruiting players."
FIFA, meanwhile, told The Guardian that it does not comment on ongoing investigations, nor can it confirm whether an investigation is ongoing.
