MacDonald, who turned 33 last week, was put on waivers by Detroit this weekend. The Pictou, N.S., native has appeared in 101 NHL games in total, spent with the Red Wings, Boston, Toronto and the New York Islanders.
MacDonald's record is 31-48-13 with two shutouts, a 3.04 average and .903 save percentage. He was out with a back injury before the Wings activated him.
Calgary is currently without star goaltender Miikka Kiprusoff due to a lower body injury. The Finnish netminder has started over 85 per cent of the team's games since 2003-04. He is scheduled to come off injured reserve later this week.
Leland Irving has played in net as the team's split its last two contests, allowing eight goals with an .867 save percentage.
The Flames signed Danny Taylor last week in the aftermath of the Kiprusoff injury, but he has no significant NHL experience.
Calgary begins a three-game homestand Monday against Minnesota.