Coburn's injury is to the left foot and he has been out of action for the last six games. He was previously thought to be close to a return, according to NJ.com's Randy Miller.
The team declined to specify the nature of MacDonald's injury, other than that it is to the "lower body." MacDonald has appeared in all of the Flyers' games to date and has recorded three points. He is second on the team in ice time, with 22:55 minutes per game.
Coburn and MacDonald were first and second, respectively, in average ice time for the Flyers last season.
The injuries leave the Flyers without three of their top defensemen. Veteran Kimmo Timonen has a career-threatening blood clot condition.
Flyers forward Vincent Lecavalier did return to practice Friday for the first time since injuring his foot on Oct. 11.
- Josh Sanchez