Herron will be the backup running back to Frank Gore with Ahmad Bradshaw being placed on IR due to a wrist injury, ESPN reports.
Herron was with the Colts until he was released in September. He then signed with Buffalo until he was released by the Bills in November. He re-signed with the Colts last week and is now the No. 2 running back. It's possible he could split any backup carries with Zurlon Tipton however.