The team confirmed on Tuesday that Pierce "sustained torn ligaments and a torn muscle in his left foot as a result of Friday’s game."
"Buck will be in a walking boot for at least the next week and we have full confidence he will do everything in his power to be back on the field as quickly as possible," Joe Mack, the Bombers' vice-president and general manager, said in a statement.
Pierce was hurt during the Bomber's humiliating 42-10 loss to the Edmonton Eskimos on Friday.
Alex Brink will be the starter for Wednesday's game in Toronto against the Argonauts.
This will be the ninth game in 24 starts that Pierce, 30, has been knocked out by injury.
"It's frustrating, you know, I'm not the only guy that gets hurt," Pierce told reporters in Winnipeg.
"This is a game that you put your body on the line … you love football, and sometimes football doesn't love you back."