AZ have failed to replicate the form enjoyed under Louis van Gaal last season and a 2-1 home defeat against Vitesse Arnhem last night was the final straw for the club's board.

The loss was AZ's seventh in 16 league games this season and leaves them in sixth place, 16 points behind leaders FC Twente and all but out of the title race before Christmas.

AZ also failed to reach the knockout stage of the Champions League under Koeman, while anything less than a win against Standard Liege in midweek will see them fail to gain the consolation of a place in the Europa League.

A statement on AZ's official website this morning read: "Ronald Koeman leaves AZ with immediate effect.

"The board and directors no longer see any basis for further cooperation."

Koeman joined the club in June on a two-year deal as the replacement for Van Gaal, who joined German outfit Bayern Munich on the back of guiding AZ to their first league title for 28 years.

AZ confirmed Koeman's assistant Tonny Bruins Slot had also left the club, and that control of the first team would pass to the remaining coaching staff.