Pittsburgh placed quarterback Dennis Dixon on injured reserve with a knee injury, which means the team will go with Roethlisberger, Charlie Batch and Byron Leftwich as its three quarterbacks for the remainder of the 2010 season.
The Steelers also signed defensive tackle defensive tackle Steve McLendon on Saturday from the practice squad.
Dixon was hurt in the Steelers' Week 2 win over the Tennessee Titans.
After recent surgery, it was discovered that Dixon's recovery would take about six weeks, which was longer than expected. That was enough to sway the Steelers (3-0) to move on with three healthier quarterbacks.
At the start of the regular season, Batch was the favorite to be released once Roethlisberger returned from his four-game suspension.
But his veteran leadership and play last week, throwing for three touchdowns in a win over the Tampa Bay Buccaneers, also helped convince Pittsburgh it's better to keep Batch around as a veteran backup.
In two starts this season, Dixon threw for 254 yards and one interception. The former fifth-round pick will be a restricted free agent after this season.
James Walker covers the AFC North for ESPN.com.