Head coach Mike Tomlin confirmed the injury, which occurred during a joint practice with the Buffalo Bills, following Wednesday's session. Warren is tentatively expected to be sidelined for four weeks.
The Steelers begin the regular season Sept. 7 against Cleveland.
Warren, entering his 10th season as the Steelers' long snapper, had both his 2008 and 2009 campaigns cut short due to knee injuries. He has played in all 64 of Pittsburgh's games over the last four years, however.