The Rovers midfielder sustained an ankle injury in the first half of the draw with Derby County a week ago, but the prognosis is that he might not make it back before the end of the season.
Speaking on Friday, Rovers boss Gary Bowyer confirmed: "At the beginning of the week we thought it was going to be a bit more positive than what it is.
"He's had it re-scanned and we now expect him to be out for a few months.
"He'll have an operation on Monday so hopefully that will speed up the recovery process with an outside chance of him being back for the end of the season."
The first match Marshall will miss is this weekend's home game against Blackpool, and one player that will also be absent is fellow midfielder Lee Williamson.
Williamson left the Oakwell pitch on a stretcher in midweek after suffering mild concussion which means he miss the Lancashire derby.
"Willo probably won't be available just on medical grounds," confirmed Bowyer.
Tickets for Saturday's match against Blackpool are currently on open sale. Tickets are priced from £19 for Adults, £12 Seniors and £7 Juniors. Why not book online today and collect your tickets from the Blackburn End collection point on the day of the game.