Retkofsky (6-5, 260) spent the 2007 training camp with the Steelers after originally signing with Pittsburgh as an undrafted rookie from TCU in 2007. He was released during the preseason.
Retkofsky, who also served as a reserve defensive lineman for the Horned Frogs, will wear jersey No. 61 for the Steelers.
Warren, who injured his left knee against the New York Giants, is out for the remainder of the season.
The Steelers also announced that first-year punter Ricky Schmitt has been added to the team's practice squad. Schmitt (6-3, 202) was in training camp with the San Francisco 49ers in 2008. He originally signed with the Arizona Cardinals as an undrafted rookie free agent from Shepherd College in 2007. He was released in training camp both times.