The Guernsey police said that after scouring for 15-hours, the rescue teams saw "a number of floating objects" in the water.
French and British authorities are conducting a massive search for the Piper Malibu aircraft that lost radar contact off the coast of the island of Guernsey near the stormy Channel overnight.
Sala joined FC Nantes in 2015 and has scored 42 goals for the club.
A large-scale sea and air search was immediately launched but called off several hours later due to strong winds and worsening sea conditions.
He expects the search operation to resume when visibility improves on Wednesday morning.
Sala returned to the French city to say goodbye to ex-teammates on Monday before boarding the plane to Cardiff in the evening.
The 28-year-old Argentinian striker completed a move to the Premier League club at the weekend but had returned to France, where he had been playing for Ligue 1 side Nantes. "We are very concerned for the safety of Emiliano Sala".
"So far over 1,000 square miles have been searched by a total of five aircraft and two lifeboats", Guernsey police said.
Jesus. Pies aren't the praying type, but we've got everything crossed that they find the missing people, whether they be professional footballers or otherwise.
The weather conditions are better now, but the seawater is not very warm.
It was added that if the plane had landed on the water, the chances of survival were "slim".
"Sadly we are fearing the worst.the sea temperature is so cold at the moment", John Fitzgerald, Chief Officer of Channel Islands Air Search, told news agency AFP. Jersey ATC lost contact whilst it was flying at 2300 feet.
FC Nantes and Cardiff city officials did not immediately comment.
"We still have crews out searching, and once they return later today (Wednesday) they will file a report, at which point we hope to issue a full statement".