Cardiff City have been left shocked and dismayed after Nantes demanded the first instalment of the transfer fee for Emiliano Sala, who was on board a plane that went missing a little over a fortnight ago.

It is understood that Cardiff received a letter from Nantes on Tuesday, in which the French club threatened to take legal action if the first scheduled payment is not received within the next 10 days.

Although Nantes were entitled to the first slice of Sala’s reported £15m fee by now, there is a sense of disbelief at Cardiff given the circumstances and the timing. The plane that Sala was travelling on was only discovered on Sunday and the Air Accident Investigation Branch (AAIB) has not said whether the body spotted in the wreckage, which was found on the seabed, is that of the Argentinian striker or David Ibbotson, the pilot.

Nantes emailed Cardiff last Thursday in relation to the payment terms and the Welsh club’s failure to transfer the first of three instalments. They then followed up that message five days later with a more direct demand that referenced possible legal action.

From Cardiff’s point of view, the priority is to establish all the facts around the tragedy. There is no suggestion that the Welsh club will not meet their contractual obligations, but at the moment there is a desire and determination to gather all the relevant information first – and that could mean waiting until an official investigation is completed.

Play Video 2:09 Emiliano Sala: body found in plane identified as missing footballer – video report

Sala was insured by Cardiff after signing for the club on 19 January, two days before his ill-fated flight back from Nantes, where he had returned to say goodbye to his former teammates. It is believed that Cardiff have a player insurance policy of £16m per individual and that Sala was registered under those terms on the morning of 21 January.

Yet many grey areas remain and unless Cardiff change their stance, which seems unlikely, there is the potential for the two clubs to become embroiled in a long-running dispute. To complicate matters further, Bordeaux, the French club Sala switched from to join Nantes, are also entitled to a significant percentage of the transfer fee – possibly as much as 50% – after inserting a sell-on clause back in 2015.

All the while, the AAIB is continuing with their operation, after the plane was found 67m underwater, 21 miles off the coast of Guernsey in the English Channel. An official search for the Piper Malibu was called off on 24 January, when Guernsey’s harbour master, David Barker, said the chances of survival after such a long time were extremely remote.

A privately funded search for the plane, backed by Sala’s family and thousands of people who donated money as part of a crowdfunding exercise, got underway on Sunday, and the plane was found within two hours.

Conditions, however, are far from ideal. An AAIB spokesman said: “We are attempting to recovery the body. If we are successful, we will consider the feasibility of recovering the aircraft wreckage.Strong tidal conditions mean we can only use the remotely operated vehicle for limited periods each day and this will mean that progress is slow. Regardless of the results, we will not be making a further statement until the families have been informed.”