Koeman failed to impress at Alkmaar after being appointed as manager at the club just six months ago.
A statement on the club’s website confirmed: “The management no longer see on what sporting basis our relationship with Koeman can continue.”
“I’m disappointed with this decision,” said Koeman.
“I had the impression that things were coming together over the past few weeks and that the management had confidence in me.
“Friday’s game against Vitesse was bad, I accept that. But this ddecision has disappointed me greatly.”