Toronto Argonauts head coach Ryan Dinwiddie confirmed a diagnosis of a torn pec for running back Andrew Harris.
The 35-year-old Winnipeg native is expected to miss four to six weeks, but season-ending surgery isn't out of the question.
Harris left last Friday's 34-27 loss to the Hamilton Tiger-Cats early.
Harris is in his first season with the Boatmen after having spent the previous five years with his hometown Blue Bombers.
In eight games this year, Harris rushed for 490 yards on 114 carries. He added another 180 yards receiving on 23 receptions.
Dinwiddie also announced a groin injury incurred during warm-ups against the Ticats will sideline receiver Cam Phillips for three to four weeks.
The Argos (4-4) are next in action on Saturday when they host the Calgary Stampeders (5-3) at BMO Field.