"I've been playing football at the level I want to play, but to continue playing at that level, I needed this week off," Cornish told reporters Friday in Calgary.
"I've had a few things accumulate playing some tough teams and needed some time. I would say this is more precautionary than anything."
Cornish missed six games in July and August with concussion-like symptoms, but has been on a tear in the four contests since his return.
The CFL's most outstanding player and top rusher last season ranks third in league rushing with 587 in five games.
Calgary leads the West Division standings with a CFL-best 10-1 record.
The Stampeders will also be without starting quarterback Bo Levi Mitchell in Montreal.
Mitchell is recovering from a sprained ankle and stretched ligament in his left knee. Drew Tate will get his first start of the season.