Horton suffered the injury in the Redskins' loss to the Lions on October 31. At the time, it was diagnosed as a high ankle sprain. Horton had fallen out of the safety rotation under defensive coordinator Jim Haslett and had just seven tackles in seven games this season.
The Redskins will promote Anderson Russell to the 53-man roster to replace Horton. The team also signed wide receiver Taurus Johnson, who played his college ball at South Florida, and Sha'reff Rashad, who played for Central Florida, to the practice squad.