I wasn't given enough time to succeed - David Moyes
The Scot was sacked in April, not even getting the chance to see out a full season in charge as Alex Ferguson's replacement as United made a shocking defence of their Premier League title.
It left United officials - Ferguson included - red-faced after Moyes had been installed as 'the Chosen One', with the former Everton boss becoming 'the sacked one' before the season was out, at a club famed for giving managers time.
Moyes was accused of bungling in the transfer market but claims he tried to sign Cesc Fabregas, Cristiano Ronaldo and Gareth Bale.
Louis van Gaal has since moved into the dugout at Old Trafford and Moyes is now ready to return to management, but insists he was not given the time needed to get to grips with one of world football's most high-profile jobs.
He said: "It was a step into the unknown and, looking back now, it was near enough the impossible job.
"But it was the right job for me. I'd been at Everton for more than 11 years. We'd qualified for the Champions League, got to an FA Cup final, I'd been voted manager of the season three times.
"I was devastated to lose the job because it was something I felt I could make a real success of. We knew it was going to take time to make the necessary changes. It was going to take time to evolve. But we were in the process of making other important changes. In the end, I don't feel I was given time to succeed or fail."
The failure to significantly improve the squad Ferguson left him also hindered Moyes who, along with chief executive Ed Woodward - also new to the role - missed out on a number of targets.
"It's been well documented that we wanted Fabregas, Bale and Ronaldo. There was talk of Ronaldo when I first arrived. We were close to getting a couple of major names," he said.
"I'm not getting in a blame game here but things just didn't materialise. I had taken over from the most successful manager in history. The chief executive had taken over from one of the most renowned administrators in the game (David Gill). So it was a new job for two people."
Moyes insists he always had Ferguson's backing.
"I've met Alex on several occasions since I left," he added. "At no time did I ever have anything other than 100 per cent support from him. He was always incredibly good to me."