The 28-year-old Argentina-born forward had been en route from Nantes in western France with pilot David Ibbotson to make his debut for Welsh team Cardiff City when the plane disappeared over the English Channel on Jan. 21.
Britain's Air Accidents Investigation Branch (AAIB) said it was informed on Monday that part of a seat cushion had been found on a beach near Surtainville on the Cotentin Peninsula in northern France.
A second cushion was found in the same area later that day.
"From a preliminary examination, we have concluded that it is likely that the cushions are from the missing aircraft," the AAIB said in a statement.
Investigators said they now planned to launch an underwater seabed search for aircraft wreckage. Due to weather conditions, the search would start at the end of this weekend and take up to three days.
"Based on a detailed assessment of the flight path and last known radar position, we have now identified a priority search area of approximately four square nautical miles," they said.
A remotely operated vehicle will be used to examine visually any wreckage found.
A privately funded operation is also set to search for wreckage on Sunday and the AAIB said it was liaising closely with those involved.
Sala had been travelling from Nantes to make his debut for Premier League side Cardiff City after being signed for a club record fee of 17 million euros (15 million pounds).
Rescuers scoured about 1,700 square miles after the single-engined Piper Malibu plane went missing but had failed to find a trace of the aircraft until now.
The plane had been cruising at 5,000 feet (1,525 m) when the pilot requested to descend to a lower altitude on passing Guernsey. It then lost radar contact at 2,300 feet.
On Tuesday, Cardiff played their first game since Sala's disappearance, a 2-1 Premier League defeat at Arsenal, where tributes were paid to the missing player and pilot.
(Reporting by Kate Holton/Alan Baldwin; editing by Stephen Addison/Ken Ferris)
