Veteran back-up Byron Leftwich will make his first start for the Steelers, replacing the two-times Super Bowl winner Roethlisberger.
Roethlisberger sprained the sternoclavicular joint in his right shoulder against the Kansas City Chiefs on Monday when he was sacked by linebacker Justin Houston in the third quarter.
Leftwich came in for Roethlisberger, going 7-for-14 for 73 yards in his first regular season game in almost two years.
The Steelers won 16-13 after an over-time field goal.
The 32-year-old Leftwich was drafted by the Jacksonville Jaguars with the seventh pick of the first round of the 2003 draft but was cut in 2007 and has mainly been a back-up since with Atlanta and Tampa Bay, as well as an earlier spell at Pittsburgh.
While Leftwich is an experienced back-up, the loss of Roethlisberger is a major blow for the Steelers (6-3) who trail the Ravens (7-2) in the AFC North.
After facing the Ravens at home, Pittsburgh have another divisional game at the Cleveland Browns before travelling to Baltimore for the return game on December 2.