De Boer has had the final year of his contract cancelled after telling the Ajax board he wanted to go in the wake of Sunday's dramatic collapse in the Dutch title race.
Failure to win at De Graafschap handed PSV the Eredivisie and made it a second straight season without the title for the former Netherlands captain, who delivered four in a row following his 2010 appointment.
De Boer's agent said earlier this month the 45-year-old would "love to join a club like Everton".
It is understood Everton had Rafa Benitez in their sights.