As expected, Sergiño Dest, 19, has signed a five season deal with FC Barcelona, making him the fourth key Ajax player to leave the squad during the current transfer period.
Right back Dest, who earlier opted to play internationally for the US rather than the Netherlands, came up through the Ajax youth training programme and joined the top team last season. Bayern Munich were also interested in the youngster.
The transfer sum has been put at some €20m, but that could increase with bonuses, broadcaster NOS said.
Hakim Ziyech (Chelsea), Donny van de Beek (Manchester United) and Joël Veltman (Brighton & Hove Albion) have all left the Amsterdam club this season.