Turkey international Erkin, 31, joined Inter Milan in the off-season before 2016-17, right when de Boer was appointed as Roberto Mancini's replacement at the helm.
De Boer was not a fan and immediately sent the left-back on loan to Besiktas. Erkin never returned to San Siro and never made an official appearance for the club.
De Boer, meanwhile, was sacked just five games into the season - a short but dreadful spell in Inter's history - and Erkin has revealed his intense dislike of the Dutchman.
“I thought it was going to be my big career step - that I could play regularly, win trophies and earn the affection of the Inter fans,” said Erkin to FCInterNews.it.
“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 like 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 got from de Boer was totally disrespectful and he transformed my career path 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.
"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 [former Inter teammate] 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.”
De Boer had a successful start to his coaching career with Ajax, winning four consecutive Eredivisie titles, but after his woeful Inter spell he also had a terrible time in charge of Crystal Palace in the Premier League.
The Eagles sacked him after just 10 weeks - the shortest reign in the Premier League era - in which time they lost four matches in a row without scoring a single goal.
He is currently the head coach at Atlanta United in the United States' MLS.
