Ronald Koeman has revealed that the writing was on the wall at Everton as early as pre-season.

The Dutchman was sacked as manager after 16 months in charge after the 5-2 home defeat to Arsenal left the Toffees languishing in 18th place in the Premier League.

Koeman, who has now been replaced by Under-23s boss David Unsworth on an interim basis, spent extensively in the summer but lost star striker and top scorer Romelu Lukaku to Manchester United.

Who could replace Ronald Koeman as Everton manager? Show all 9 1 /9 Who could replace Ronald Koeman as Everton manager? Who could replace Ronald Koeman as Everton manager? David Wagner SWANSEA, WALES - OCTOBER 14: David Wagner, Manager of Huddersfield Town looks on during the Premier League match between Swansea City and Huddersfield Town at Liberty Stadium on October 14, 2017 in Swansea, Wales. (Photo by Gareth Copley/Getty Images) Getty Images Who could replace Ronald Koeman as Everton manager? Duncan Ferguson LIVERPOOL, ENGLAND - DECEMBER 19: Everton coach Duncan Ferguson looks on prior to the Premier League match between Everton and Liverpool at Goodison Park on December 19, 2016 in Liverpool, England. (Photo by Michael Regan/Getty Images) Getty Images Who could replace Ronald Koeman as Everton manager? Eddie Howe BOURNEMOUTH, ENGLAND - SEPTEMBER 30: Eddie Howe, Manager of AFC Bournemouth looks on prior to the Premier League match between AFC Bournemouth and Leicester City at Vitality Stadium on September 30, 2017 in Bournemouth, England. (Photo by Steve Bardens/Getty Images) Getty Images Who could replace Ronald Koeman as Everton manager? Mikel Arteta BLACKBURN, UNITED KINGDOM - DECEMBER 03: Mikel Arteta of Everton celebrates his goal during the Barclays Premiership match between Blackburn Rovers and Everton at Ewood Park on December 3, 2005, in Blackburn, England. (Photo by Clive Mason/Getty Images) Getty Images Who could replace Ronald Koeman as Everton manager? Paulo Fonseca ROTTERDAM, NETHERLANDS - OCTOBER 17: Paulo Fonseca, Manager of Shakhtar Donetsk gives his team instructions during the UEFA Champions League group F match between Feyenoord and Shakhtar Donetsk at Feijenoord Stadion on October 17, 2017 in Rotterdam, Netherlands. (Photo by Dean Mouhtaropoulos/Getty Images) Getty Images Who could replace Ronald Koeman as Everton manager? Sean Dyche BURNLEY, ENGLAND - SEPTEMBER 19: Sean Dyche manager of Burnley looks on before the Carabao Cup Third Round match between Burnley and Leeds United at Turf Moor on September 19, 2017 in Burnley, England. (Photo by Nathan Stirk/Getty Images) Getty Images Who could replace Ronald Koeman as Everton manager? Sam Allardyce LONDON, ENGLAND - MAY 14: Sam Allardyce, Manager of Crystal Palace looks on prior to the Premier League match between Crystal Palace and Hull City at Selhurst Park on May 14, 2017 in London, England. (Photo by Steve Bardens/Getty Images) Getty Who could replace Ronald Koeman as Everton manager? Carlo Ancelotti PARIS, FRANCE - SEPTEMBER 27: Carlo Ancelotti, head coach of FC Bayern Muenchen looks on prior to the UEFA Champions League group B match between Paris Saint-Germain and Bayern Muenchen at Parc des Princes on September 27, 2017 in Paris, France. (Photo by Alexander Hassenstein/Bongarts/Getty Images) Bongarts/Getty Images Who could replace Ronald Koeman as Everton manager? David Unsworth BOLTON, ENGLAND - AUGUST 30: David Unsworth, coach of Everton looks on during the Checkatrade Trophy group match between Bolton Wanderers and Everton under-23s at Macron Stadium on August 30, 2016 in Bolton, England. (Photo by Nathan Stirk/Getty Images) Getty

And the 54-year-old believes it was the failure to adequately replace the Belgian, specifically with Arsenal's Olivier Giroud, was the precursor of what was to come.

“I had Olivier Giroud in the building. He would have fitted perfectly, but at the very last moment he decided that he’d rather live in London and stay at Arsenal," he told the Daily Mirror. “That was really hard to swallow. You tell me, where you can get a better striker?"

Koeman also points to his team's tough opening fixture schedule where they face five of last season's top six as another key factor behind the slow start that ultimately cost him his job.

“I looked at it and saw that five of our first nine games would be against clubs from last season’s top six: Chelsea, Tottenham, Man City, Man United and Arsenal," he added. “I looked at it again and I said to myself, 'Phew!'

"That is not going to be an easy run, in particular with a Europa League run at the same time and a really early start with all the players because of the European games. And most of all, because I had lost my striker Lukaku.’’

Koeman's successor Unsworth is the bookmaker's favourite to take up the job on a permanent basis and revealed following the 2-1 defeat to Everton on Wednesday evening that he is set for talks with owner Bill Kenwright on Friday to discuss his future.

The defeat to Arsenal proved to be Koeman's last game in charge (Getty)

“I honestly don’t know,” Unsworth replied when asked what sort of criteria he had been set. “All I know is that we’ll hopefully be as committed as that every game that I’m in charge. There’s an awful lot to work with there. It’s a very proud performance tonight.

“I’m scheduled to meet [Kenwright] on Friday afternoon. I speak to the chairman three or four times a day. The communication is brilliant. I’ve got a great relationship with the board. What will be will be. There’s no points return or games total that they’ve set. I just have to be committed. We have to try to win some games and take it from there.