At least a few of the Everton squad may fear for their future following the departure of the Dutchman.
A report in The Mirror claiming that former Borussia Dortmund coach Thomas Tuchel is the frontrunner to replace the Dutchman should get the Goodison Park faithful excited.
But some of Koeman's Toffees favourites may be more apprehensive about their futures under a new boss.
The full-back was a trusted servant of Koeman, who signed him for Southampton and for Everton.
But his performances at both clubs have proven that he is simply not good enough to help the Toffees compete with the Premier League big boys, and any new manager will likely suss that out quickly.
Vlasic is another who had the faith of Koeman, but his performances warranted it. The 19-year-old has showed real promise in his handful of appearances and is definitely one for the future.
However, Koeman’s replacement will want to hit the ground running and might dump Vlasic for more experienced attacking midfield options such as Kevin Mirallas or Davy Klaassen.
By the end of Koeman’s time at Goodison Park, the Frenchman was only making the team on reputation.
His recent displays have not been anywhere near the standard he set when being courted by Manchester United, and now he does not have his former Southampton boss to protect him.