Dick Advocaat walked out on Sunderland after coming to the conclusion the squad was "not good enough" and admitted a relegation scrap was "not his cup of tea".
Advocaat's resignation was confirmed on Sunday, 24 hours after his final game of a seven-month tenure ended in a 2-2 draw against West Ham.
The Dutchman has cut a forlorn figure during the Wearsiders' abysmal start to the season - they have failed to win any of their opening eight Premier League games - and revealed he had made up his mind to go prior to the weekend.
He told Studio Voetbal: "I already made my decision last week. But the club asked me to do the match versus West Ham, and I really wanted to finish in style.
"The struggle against relegation is not my cup of tea. I think it was time for someone else to take over at Sunderland. I became negative, and that didn't feel like myself."
Advocaat initially moved to Sunderland in March with the brief of maintaining the club's top-flight status, a task he achieved with a game to spare.
Having initially refused the offer of a new deal, he was persuaded to sign a one-year contract after reportedly receiving assurances over the club's summer transfer budget from owner Ellis Short.
And while Advocaat stopped short of criticising Short, he conceded a figure of how much they had to spend was never given.
He added: "I don't regret signing my new contract, because it was a great experience.
"Our squad was simply not good enough. The club knew that we had to strengthen, but the chairman never told me how much we could spend."
The search for a new manager at the Stadium of Light has now started with Burnley boss Sean Dyche, Sam Allardyce and Nigel Pearson the early front-runners.
