The 32-year-old is keen to focus on his club career with Birmingham but also expressed fears over a media frenzy if he did play for Scotland again.
He told the Daily Record: "It has not been an easy decision for me to make but I feel I have done the right thing.
"There was a danger that, by returning now, I would have started a media frenzy and it would have been a distraction for the rest of the boys and the manager. That would not have helped anybody.
"Yes, it is hard to say no to Scotland because it hurts not to be involved with the national team. But I believe in fate and things happen for a reason.
"I want to enjoy my time here [at Birmingham] but I wish Scotland all the best."