Rafael Benitez says his decision to walk away from Newcastle came after he lost trust in the club's hierarchy.
Benitez left the club on Sunday after his contract came to an end, with the two parties unable to reach agreement over extending his three-year spell at St James's Park.
The Spaniard wrote an open letter to Newcastle fans on Monday, saying he would have stayed at the club if he felt they shared his "vision", and he has expanded on his reasons for leaving in an interview with The Times.
Asked if he lost trust in those in charge at Newcastle, Benitez said: "Yes. We didn't have that, so I had to choose.
"Obviously, I had the feeling they were really pleased for me to stay at the beginning, but later on, when we had different views in terms of how to move forward, I couldn't see this support. I couldn't see this clear desire I could feel at the beginning."
Benitez won the Championship in his first full season at Newcastle before achieving two mid-table finishes in the Premier League, despite the club generating a profit in the transfer market during his time in charge.
While he says he wanted the club to invest in order to move up the table, Benitez says: "I didn't ask for any money. I just wanted to know how much [there was].
"The club put out some information about the budget being around £50m, plus the money from sales, and that was fine.
"I wasn't complaining. I knew it was the reality. But to have a chance, to compete in cup competitions, to be closer to the top, where Newcastle deserve to be, you have to do things really well.
"The reason I wasn't happy was because we weren't competing. We could have done more with the resources we had."
Benitez has already accepted a new role as manager of Chinese side Dalian Yifang, while Porto boss Sergio Conceicao is believed to be keen on replacing him at St James' Park.