The 27-year old winger left the Dutch giants in the summer to sign with Celtic for around £3million and de Boer suggests it was not for a lack of him trying to get the former Waalwijk and Zwolle man's head right.
"I gave Derk many opportunities at Ajax but it didn't work out," he told the Daily Record.
"We looked into the future and saw more in the young players at the club.
"He also didn't have the best of luck with injuries and he wasn't very self-critical.
"In situations like that you must look at yourself and if there is a player behind you who is coming through, then you need to raise your game.
"That aspect of his game could have been better."
Since joining the Hoops, Boerrigter has made just five starts for a total of 10 appearances and is yet to score a goal.
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