"Chris Killen has been flying in pre-season but the decision was made at the end of last season for him to go as one of the over-age players for New Zealand," McDonald told the Daily Mail. "It will be a fantastic experience. I got the option to go, as well, but declined.
"The offer was tempting but I felt it was more important for me to get my foot in the door again (at Celtic) and make sure nobody can take my place. The most important thing for me is my career with Celtic and I never want to jeopardise it.
"I was dropped for the last Olympics when I was with Motherwell and it would have been massive to play this time. Hopefully, there will be another chance for me and, if not, there's a World Cup in two years.
"What's more important to me is the Champions League and winning more honours with Celtic. That's why I signed on at the club for another five years."