Torain, who led the team in rushing last season with 742 yards and four touchdowns, was slowed by a fractured hand he suffered in training camp.
In eight games this season, Torain totaled 200 yards on the ground with one touchdown.
Meanwhile, rookies Roy Helu and Evan Royster have emerged as productive running backs.
Helu leads the team in rushing with 635 yards and two touchdowns. He also has 47 receptions for 331 yards. Royster has 215 yards rushing in five games.
Wide receiver Aldrick Robinson will replace Torain on the active roster. Washington also added running back Stafon Johnson to the practice squad.