Klaassen was signed by Koeman last summer for a fee in the region of €27 million but has been unable to break through as had been expected of him.
A foot injury ruled the former Ajax man out of the next two games and by that time, Koeman’s job was in trouble and opted for his more ‘tried and tested’ players whilst Klaassen was relegated to the bench.
Speaking to Ziggo Sport on Sunday, Koeman said: “I called him a few weeks ago and spoke out of curiosity. He was in the picture again at Everton, but now again not.
“I do not know why.”
The current Netherlands boss opened up on the midfielders struggles, stating: “He had a difficult start at Everton, that was disappointing but you can not say that he does not train hard and works hard.”
Klaassen has only made five Premier League appearances with his last coming in the win over Brighton and Hove Albion yet, he hasn’t been named in a matchday squad since the defeat to Manchester City that following week.
“Disappointed with Davy”
Despite a January loan move to Napoli falling through, Klaassen’s agent revealed he was ‘keen to fight for his chance’ to show what he can before the season ends.
There have been plenty of calls from fans to see the 25-year-old given a chance before the campaign comes to a close but current boss Sam Allardyce has been reluctant to answer those calls.
Former boss Koeman admitted that Klaassen had "trouble" with the change in “aggressiveness and the tempo,” of the Premier League compared to the Eredivisie.
“You do not get time on the midfield. I was disappointed with Davy,” Koeman said.
“What did not help him was that we did not have a striker.”
Romelu Lukaku departed for Manchester United and the Blues attempted to replace him with Olivier Giroud but the deal for the Frenchmen fell through despite visiting Finch Farm with hopes of completing a deal.
However, the 55-year-old admitted that he "really expected" the former Ajax captain to "adapt more easily" to his new home.
“Nobody in the club had doubts about him,” added Koeman. “Not in the Netherlands either.”