The team announced Friday it had doubled up in its attempt to find a consistent snapper for punts and place kicks.
The Seahawks have used six long snappers in three years since Jean-Philippe Darche left in free agency for Kansas City following the 2006 season.
They brought Jeff Robinson out of retirement three times to do the job, including last fall.
MacDonald snapped in the Canadian Football League with Winnipeg and Calgary. The native of Toronto had NFL tryouts with Carolina and New Orleans.
Copyright 2010 by The Associated Press