The French Aviation Authority has confirmed Cardiff City striker Emiliano Sala was on board a light aircraft that went missing near the Channel Islands last night.
The Welsh club's chairman Mehmet Dalman says they are very concerned, but are awaiting further confirmation.
The 28-year-old Argentine striker completed a £15 million move from Nantes on Saturday and was due to report for training with Cardiff this morning.
Sala scored 12 goals in 19 Ligue 1 games for Nantes this season.
They were due to play in the French Cup tomorrow, but the game has been postponed.