The Atlanta coach lasted only months in charge of Inter.
Erkin joined Inter in 2016, but was immediately loaned out by De Boer to Besiktas.
He told FCInterNews: “I thought that this was going to be the big career step, that I could play regularly, win trophies and gain the affection of the Inter fans.
“I didn't want to leave Inter, not even when Roberto Mancini left, but Frank de Boer's attitude towards me was awful. He left me out as if I was some teenager promoted from the youth academy. It was unacceptable.
“Mancini played me in pre-season, he had faith in me and I was very sad when he left. The treatment I received from De Boer was totally disrespectful and he transformed the path of my career with his attitude.
“I never understood why De Boer treated me like that. I was never in his plans, from the first day he set foot in Italy. He left me out of the final pre-season match, then didn't even let me participate in the training ground exercises. I had to train separately from the rest of the squad.
“I think he was trying to manipulate me into feeling so frustrated that I'd walk away. I just can't explain it."
Erkin added: “Everyone knew what kind of person De Boer was, that's why I still can't figure out how he managed to reach a club like Inter.
“I agree with Jonathan Biabiany when he says De Boer was the worst coach in the history of Inter. It's awful that all my dreams were shattered by a man who was only there for two-and-a-half months."
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