Cardiff City have reportedly contacted the police as they want further information relating to Emiliano Sala's £15m transfer from Nantes.
The Argentine striker died when the single-engine plane ferrying him across the English Channel to Cardiff crashed into the sea on January 21.
Nantes have asked Cardiff for the first £5m payment for Sala, who never got to play for his new club, but the Bluebirds will first conduct their own investigation.
According to The Sun, Cardiff have involved the police, FIFA and the Football Association as part of their probe into the circumstances around the ex-Nantes ace's disappearance.
City are said to have also written to the French club to answer a handful of questions, one of which asks whether they believe Sala was a Cardiff player the night he stepped on to the fatal flight, and whether he was third-party owned.
Questions have also been asked of agent Willie McKay and how much he profited from the transfer.
Sala's funeral took place on Saturday in his hometown of Progreso.