The full-back joined Ross County on a two-year deal after his contract in Glasgow expired at the end of May.
Foster maintains he only found out he would not be offered extended terms at Ibrox through an article in a newspaper.
Other players among the group of 11, including striker Jon Daly, are also known to be disappointed at not being told officially by the club his time there would be ending.
Former Aberdeen defender Foster has echoed comments from new Kilmarnock striker Kris Boyd – another of those who have departed Rangers – with his views on the situation.
He told the Daily Record: “I haven’t heard a thing from Rangers. I just thought it would be common courtesy to say: ‘Thanks for your service and all the best.’
“But we’ve had nothing from the club. I found out I was going by reading King’s comments on the back of a paper. He said none of us were good enough and we weren’t getting a new contract.
“I don’t judge him on his business acumen and he has never really seen me play so he shouldn’t judge me on my football ability.
“Effectively, the 11 of us got blamed for the season but there were many different factors. To single out the players who left was a bit harsh.
“He also did it in a way we couldn’t really respond, except in the press. Did it leave a sour taste? Yeah, a little bit.
“That’s not how you should run a business or a club. If that’s the way he wants to do it fair play to him. I don’t agree with it and never will.”