"The day I left United, in hindsight, I should have stopped playing really" Keane said in an interview with the Irish Times.
"I lost the love of the game that Friday morning. I thought football is cruel, life is cruel. It takes two to tango also. I am fully responsible for my own actions but some things are wrong.
"I left on a Friday and they told me certain things before I left that day. I was told the following week I couldn't sign for another club. I had been led to believe I could. There were certain things I was told at certain meetings that were basic lies," Keane said.
"That was part of the exit plans, I am convinced. Especially with my pride, I wasn't going to accept that. They had a statement prepared and they were thanking me for 11 and a half years of service.
"I had to remind David Gill I had been there 12 and a half years. I think that might have been part of the plan," he added.
"Then the financial stuff was mentioned. I was thinking, my God, I am happy to leave. I won't go down that road. A week later they announced £70 or £80 million profit after telling me I hadn't played for six weeks and so they weren't prepared to do this and that.
"I look back and think I should have said this and I should have said that. It is like Mick McCarthy at the World Cup. I always think when he said if you don't have respect for me you can't play for me, I should have said to him what I felt.
"I am not playing for you I am playing for Ireland. It is easy to be wise afterwards."