The clubs are wrangling over payment of the fee following the tragic death of Argentinian Sala in an airplane accident in January.

Nantes referred the matter to the sport's global body after the Welsh side declined to pay an initial six million euros ($6.8 million) of the 17 million euros ($19.4 million) total fee.

"Nantes have naturally turned to FIFA. We have bodies which can deal with these sorts of things. There's also a human aspect to the situation which makes us more than just sad. It's a tragedy," FIFA president Gianni Infantino said.

"For the rest of it FIFA bodies will take care of it and I hope both clubs will come to an agreeement," he added.

Cardiff were due to pay the initial six million euros once the transfer had been registered but the club said they wanted to wait for the results of the investigation into the accident before transferring any funds.

"Cardiff City remains committed to ensuring fairness and accountability with respect to the agreement between Cardiff City and FC Nantes, but first and foremost the relevant authorities must be allowed to determine the facts surrounding this tragedy. It is inappropriate to comment further at this stage," Cardiff said in a statement.

According to the French club, the 28-year-old's move from France had been completed and an International Transfer Certificate (ITC) issued.

As the ITC had been registered and Sala had been confirmed as a Cardiff player, according to Nantes the Welsh club were obligated to pay for the transfer.

- Mandate expired -

However, Cardiff are concerned about possible irregularities involving the flight from Nantes to Cardiff which resulted in Sala's death.

Pilot David Ibbotson, 59, was flying Sala to the Premier League outfit on January 21 when the accident happened.

Britain's Air Accidents Investigation Branch (AAIB) said on Monday the plane carrying Sala did not have a commercial licence.

But it said the journey would have been allowed as a "private" flight in which costs are shared between pilot and passenger.

It added that the basis on which Sala was a passenger had not been established.

Football agent Mark McKay had a mandate from Nantes to negotiate the transfer of the professional contract between the two clubs.

Nantes has said that the mandate had expired by the time Sala boarded the flight as he had already signed for Cardiff City.

The investigators also said that since the pilot's logbook and licence were not recovered, it was unclear whether Ibbotson was authorised to fly at night.