Redd suffered the original injury to his right knee after landing awkwardly at the end of a run against Cal on Nov. 9. He sat out games against Stanford and Colorado before returning against UCLA with five carries for 25 yards.
The Trojans had hoped to get Redd back for next Saturday's bowl game against Fresno State, but interim coach Clay Helton said that scenario is unlikely.
"Silas' knee is probably worse than expected, so we don't think he's going to make it right now," Helton said after the Saturday practice with Redd watching from the sidelines in sweatpants.
It has been an injury-plagued year for Redd. In addition to the current injury, he also missed the first five games of the season after an injury to his left knee in spring ball.
If he misses the bowl game, Redd will finish the 2013 season with 376 yards on 81 carries with one touchdown.
Redd transferred to USC from Penn State before the 2012 season after sanctions against the Nittany Lions were handed down. He led the Trojans in rushing in 2012 with 905 yards on 167 carries and nine touchdowns.