Donny van de Beek was left out of Ajax's squad for the Dutch champions' friendly with Eintracht Frankfurt, with a transfer potentially imminent.
New Barcelona boss Ronald Koeman wants to sign AZ Alkmaar winger Calvin Stengs.
Chelsea have expressed an interest in signing Ajax's Argentina international left-back Nicolas Tagliafico.
UEFA has advised that the 2020 summer transfer window should close no later than October 5.
Supporters will not be able to attend football matches in the Netherlands until there is a coronavirus vaccine, Dutch health minister Hugo de Jonge says.