Eliaquim Mangala’s transfer to Manchester City is being investigated by FIFA for a possible breach of third-partnership ownership rules.
Mangala joined City in the summer of 2014 in a £32million move from Porto, in a deal in which Doyen Sports received £10.6million.
The player representation company, which has bases in Malta and London, had purchased a share of the defender’s future value for just under £2million in 2011.
City themselves have not broken any rules, but the Portuguese club could be fined or placed under a transfer embargo.
After starting his career at Standard Liege, the France international move to Porto in a £11.4million deal which also included Steven Defour.
The 24-year-old has made 41 appearances for Manuel Pellegrini’s side.