Cardiff's record signing Emiliano Sala was on board a plane that went missing over the English Channel on Monday night, French media have reported.
The 28-year-old Argentinian striker completed a move to the Premier League club over the weekend but had returned to France, where he had been playing for Ligue 1 side Nantes.
French media, quoting police sources, said Sala was on the light aircraft that disappeared from radar on Monday night while apparently flying from Nantes to Cardiff.
Cardiff told the BBC that they are "seeking clarification" over what has happened.
Sala had signed a three-and-a-half year deal with the Welsh club after scoring 12 Ligue 1 goals in 19 appearances this season.
Guernsey Police posted on Twitter on Tuesday morning that the search had resumed at 8am but that there was still no trace of the plane.
It read: "Searching for the light aircraft PA 46 Malibu resumed at 8am this morning. No trace has currently been found.
"It was en route from Nantes, France to Cardiff, Wales with 2 people. More info when available."