FIFA has banned Chelsea from signing new players in the next two transfer windows after breaching rules relating to the registration of players under 18.
The ban relates to cases involving 29 young players, with the Blues having been accused of committing "several other infringements relating to registration requirements for players".
An official statement released by FIFA reads: "The FIFA Disciplinary Committee has sanctioned the English club Chelsea FC and The Football Association for breaches relating to the international transfer and registration of players under the age of 18.
"Chelsea was found to have breached art. 19 of the Regulations in the case of twenty-nine (29) minor players and to have committed several other infringements relating to registration requirements for players. The club also breached art. 18bis of the Regulations in connection with two agreements it concluded concerning minors and which allowed it to influence other clubs in transfer-related matters.
"The Disciplinary Committee sanctioned Chelsea with a ban on registering new players at both national and international level for the next two (2) complete and consecutive registration periods. This ban applies to the club as a whole - with the exception of the women’s and futsal teams - and does not prevent the release of players.
"Additionally, the club was fined CHF 600,000 and given a period of 90 days to regularise the situation of the minor players concerned."
In addition to Chelsea, the English FA has also been sanctioned, although both parties will be able to contest the decision with FIFA's Appeal Committee.
"The Football Association was also found to have breached the rules in connection with minors," the statement continues. "It was fined CHF 510,000 and given a period of six months to address the situation concerning the international transfer and first registration of minors in football.
"The protection of minors is a key element in FIFA’s overall regulatory framework relating to the transfer of players and effective enforcement of these rules is paramount, as also confirmed on various occasions by the Court of Arbitration for Sport.
"The decisions issued by the Disciplinary Committee were notified today and can be contested before the FIFA Appeal Committee."
The signing of Christian Pulisic - who will link up with his new team at the end of the season - will go some way to easing the Blues' concerns, but with Eden Hazard's future up in the air the news will be far from welcome at Stamford Bridge.
Chelsea have since announced their decision to appeal the ban but, if they are unsuccessful, they will likely have to turn to their large pool of loanees and youth products - players Maurizio Sarri has so far been unable to put to good use.
As revealed by Goal, Sarri's future in charge of the Blues is in doubt following a poor recent run of results, with the Italian having been given three games to save his job.