As well as bemoaning the lack of unity in the Boro squad, he also described the Premier League as "all about physical strength" and claimed that "the quality of life is higher in Italy".
De Roon is quoted by The Sun as saying: "It wasn't a nice year at all with Middlesbrough. There was a split between the English and Spanish speakers in the squad. We were not a stable team at all, and we were not close to one another.
"The Premier League is great to watch, because a lot happens, and the pace and intensity of matches is unlike anywhere else. But I missed tactical discipline. It is all about physical strength, and teams come up short tactically apart from the top six sides.
"I had no problem with the people in England, and it was easy as I spoke the language. But the quality of life is higher in Italy. The food, the weather, the coffee... I like the fact that people are more relaxed."
De Roon, who made his senior debut for the Netherlands last year, played 33 times last season for Boro in the top flight, scoring four goals.