Chelsea owner Roman Abramovich held secret stakes in players not owned by the club, a BBC investigation has found.
They included Peruvian winger Andre Carrillo when he twice played against them in the Champions League in 2014, according to the corporation, which said Abramovich held rights in players through a company based in the British Virgin Islands.
Any investments in overseas players would have pre-dated Fifa outlawing third-party ownership in 2015, something that was banned within the Premier League seven years earlier.
The BBC said a leak of documents – banks’ “suspicious activity reports” – revealed Abramovich was behind an offshore company called Leiston Holdings, which part-owned players Chelsea were said to have had first option of signing.
It said Leiston Holdings secured half of Carrillo’s “economic rights" in 2011 when it lent Sporting €1m (about £850,000) to help them purchase the player from Alianza Lima.
The loan was said to contain a number of clauses, one of which was that if an offer of more than €6m was made for Carrillo and Sporting did not accept it, they would have to pay Leiston 45 per cent of the value of the bid.
Sporting were also said to have agreed to pay Leiston a “risk fee” of more than €127,000 for each season Carrillo played for the club.
Leiston was said to also owned stakes in two other Sporting players – Gael Etock, who played for the club between 2012 and 2013, and Valentim Viola, who was in the squad between 2012 and 2016.
The Portuguese club’s accounts were said to show it owed Leiston €2.6m in 2014-15.
A spokeswoman for Abramovich told the BBC: “The fact that transactions may have been confidential does not mean that they were unlawful or otherwise in breach of then applicable rules or regulations.”
She said they “relate to the period before Fifa changed their rules”.
The spokeswoman added that suspicious activity reports do not mean laws or rules have been broken, saying: “The fact that we are not aware of this issue confirms that there has been no wrongdoing as no action was taken.”