The midfielder was allowed to come off contract this summer.
“I still had much more to give, but I've seen everything at Milan as a player and a man," he told Sportweek.
“It's disappointing that I was never able to work with the same coach for three or four years, because that does give a sense of consistency to your work. Instead, every new coach seems to be testing you, it's always starting from scratch, and that wastes a lot of time.
“I realised the way I was viewed had changed after my knee injury. I needed surgery and would only return in the final year of my contract.
“A club that has faith in you, that really believes in you, offers a contract renewal the moment a player returns to the field. In my case, that did not happen. There was no clarity.
“Perhaps the Milan Style has changed, but I got the feeling that I was not seen the same way after that injury."