• Investigation relates to signing of foreign players aged under 18 • Chelsea face possible transfer ban from Fifa disciplinary committee • Club say they comply with Fifa regulations when recruiting players

Chelsea have been accused, after an initial Fifa investigation, of breaking the rules on the signing of 25 foreign players under the age of 18. The number of cases could rise, with the matter now in the hands of the governing body’s disciplinary committee, which has the power to impose sanctions – chief among them a ban on transfers.

Fifa announced last September that it was looking into alleged breaches at Chelsea when it came to the recruitment of youth players from overseas – making them the first English club to face such action.

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Barcelona, Real Madrid and Atlético Madrid 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).

The initial investigation into Chelsea was carried out by the compliance unit of Fifa’s transfer matching system (TMS) and it is believed it was first alerted by the case of Bertrand Traoré, the Burkina Faso forward. He was signed to professional terms by Chelsea on 1 January 2014, the day the transfer window opened after his 18th birthday, but pictures would emerge of him playing for the club against Arsenal in a “non-competitive” game on 23 October 2011, when he was 16. The pictures came to Fifa’s attention in January 2016.

Clubs are not permitted to sign players under the age of 18 from other countries unless their parents have emigrated for reasons not connected to football or both the player and club are based within 50km of a national border. Under Fifa’s Article 19, the only other exception is for transfers within either the European Union or European Economic Area where the player is aged between 16 and 18. Fifa was concerned that Traoré, who left Chelsea for Lyon last June, did not appear to fulfil any of the exemptions.

TMS flagged a total of 25 player cases in which it thought Chelsea might have transgressed and it passed its findings to the disciplinary committee, which is searching for further examples in a forensic look at the club’s academy. It is within its remit to discard any of the original 25 cases. The disciplinary committee can examine any incoming transfer over a period of 10 years.

It has requested information from Chelsea and is in contact with the Football Association. It wants the FA to provide facts and figures for the 25 players – and possibly others – such as the registration details and the matches in which they have played. The disciplinary committee’s investigation is at an early stage but it is expected to develop quickly over the coming months.

When it has been completed it will submit its evidence to an independent panel within the disciplinary committee, who will reach a verdict. If found guilty, Chelsea would be entitled to appeal to Fifa and then to Cas.

Fifa’s principle is that a systemic breach of the rules is so serious it should entail a transfer embargo

A Chelsea spokesman said: “Chelsea FC complies with all Fifa statutes and regulations when recruiting players.”

Fifa deems there to be different levels of infringement on the regulations regarding minors, with the most serious being a breach of Article 19. Behind that there are less serious ones, some administrative, such as the failure to request authorisation through the correct channels.

Fifa’s principle, which it has established, is that – irrespective of the number of minors involved – a systemic breach of the rules is so serious it should entail a transfer embargo. The amount of cases affects the severity of the sanction but, if a club has a low number, Fifa believes it should not mean it avoids a ban. It is also understood that Fifa worries that a one-window suspension does not create harmful consequences; it can be worked around with sufficient planning.

Chelsea have argued that they had an option agreement, registered with and approved by the FA and Premier League, to secure Traoré’s registration after he turned 18 and which allowed them to play him in what were in effect considered trial games. In 2010 the club reached a settlement with Lens, which was ratified with Cas, to avoid a two-window transfer embargo that stemmed from the signing of Gaël Kakuta.

Fifa says it does not comment on ongoing investigations nor can it confirm whether an investigation is ongoing.

The Barcelona investigation was triggered by a newspaper article about the club’s signing of Lee Seung-woo – “the South Korean Messi” – aged 13. An employee at Fifa TMS read it and thought the deal might be in breach of the regulations. TMS would uncover 31 cases of potential transgressions and the independent panel would find Barcelona guilty on all 31. The club’s appeals failed and they were banned from two windows in 2015. Lee is now at Verona in Serie A.

Real’s case started at Fifa TMS in October 2013 and in January 2016 they were found guilty of violating the rules on the registration of 39 minors. They had been investigated on 70. Cas would uphold 37 of the guilty verdicts but reduced the ban to one window – January 2017 – because the infringements were deemed to be less serious than those of Barcelona.

Atlético’s numbers were the most startling in Spain, partly because of a partnership with Dalian Wanda Group, the Chinese property company. It saw many Chinese players coming to train at their academy. Fifa considered 183 cases in its final judgment; 153 would be confirmed. Atlético served their ban across both windows of last year.