"You have difficult times as a footballer, and that's what happened to me at City," he told The Telegraph.
"It was very tough, but hopefully now it's brightening up a little bit. That's behind me and I just take it as an experience. I wouldn't say I've any regrets about joining City, because sometimes people make these moves and it works out, and that's what I was hoping. It just didn't for me."
Sinclair insisted he did not join City for the money and spoke of his anger at not being given a chance at the Etihad.
"It's easy for people to say, 'Oh, he went for the money, he got the contract and is not fussed about football'," Sinclair added. "But anyone who knows me knew that I wasn't happy just signing the contract then relaxing and sitting back."