Alouettes president and CEO Patrick Boivin said the reason behind the dismissal couldn't be revealed because it could "potentially expose us at the legal level," according to Stu Cowan of the Montreal Gazette.
Boivin also said the decision wasn't related to the team's on-field performance or the impending sale of the franchise.
"A number of things were brought to my attention over the course of the last number of weeks that made it such that we had to make this decision immediate, right now," Boivin said. "It would be inappropriate to start getting into specifics of what that is.
"It has nothing to do with performance,” Boivin added. "We could have been 4-0 and the decision would have still been made."
Day-to-day management duties will be split by assistant general manager of player personnel Joe Mack, head coach Khari Jones, and director of football operations Patrick Donovan.
"Joe Mack will now have oversight of all football operations, but the team will be jointly managed with Khari Jones," Boivin said in a statement. "Specifically, coach Jones will now be responsible for our active roster on a daily basis, and Joe will oversee all player personnel and football operation matters, including salary cap, contracts, operations and logistics. Patrick Donovan remains Director of Football Operations. These are standout individuals and are steadfast on collaboratively doing what is best for this team to win."
The Alouettes are 2-2 this season after beating the Ottawa Redblacks on Saturday. They sit second in the East Division.
Reed had been with the club since 2015, first as the special team coordinator before being anointed as GM in 2016. He previously served as the Edmonton Eskimos' head coach from 2011 to 2013.
In June, Montreal parted ways with head coach Mike Sherman and promoted offensive coordinator Khari Jones on an interim basis.