Ball was tipped for big things at City while Mark Hughes was in charge.
Ball, who is now looking for another move, told the Daily Star Sunday: "When Mark Hughes took over he came to watch me in the reserves at Wigan. That weekend I was in the squad for the derby game against United.
"I managed to get on the bench and was there again for the following two games.
"I was playing really well with confidence but in training I broke a bone in a foot. I was out for six months. When Roberto Mancini took over he didn't really see me.
"I never got another chance. Mancini never talked to me.
"He called me 'You'. I don't think he even knew my name.
"Six months before I had been on the bench and now he didn't even acknowledge me. It was hard to take."