Brown (triceps) and tight end David Johnson (wrist) were placed on injured reserve Tuesday morning, and the Steelers signed tight end Richard Gordon and cornerback Isaiah Green to take their places on the 53-man roster.
Gordon played in 27 games for the Oakland Raiders the past two seasons. He started twice and recorded three receptions, including one for a touchdown.
Green was promoted from the practice squad.
The moves indicate that the Steelers are comfortable with Kelvin Beachum at left tackle moving forward.
Pittsburgh traded for Brown, the fifth overall pick in the 2007 draft, to help shore up the left tackle position following the demotion of Mike Adams.
He and Beachum vied to take over for Adams, and the competition ended two days ago when Brown re-injured his right triceps before the previously winless Steelers' 19-6 victory over the New York Jets.
Beachum, who had already been slated to start against the Jets, settled down after a shaky start, and the Steelers opted to stick with him at left tackle instead of signing a veteran free agent, such as Max Starks.
Coach Mike Tomlin said the team opted to promote Green from the practice squad instead of signing an offensive lineman because the cornerback might be able to help the Steelers on defense or special teams against the Baltimore Ravens on Sunday.
"We just decided to strengthen ourselves in the very best way possible," Tomlin said at his weekly news conference.
The Steelers signed Gordon to replace Johnson, Tomlin said, because he is a strong run blocker and has similar "attributes" as Johnson.
Both Brown and Johnson need surgery for their respective injuries, Tomlin said.
The Steelers did not give up much to get Brown in the Oct. 3 trade, as the Arizona Cardinals paid most of what is owed to him this season and received only conditional draft picks in return. Brown missed the 2012 season with a torn right triceps. He re-injured his triceps during pregame warm-ups Sunday.