Mack had seven carries for 18 yards and one reception for 17 yards in Saturday's preseason win over Pittsburgh.
While he wasn't as impressive as his first preseason game last week (five carries for 45 yards), Mack still showed a spark on several runs and was used in third-down situations with the first-team offense. He'll enter the season in the mix behind starter Frank Gore, but could find a small role initially. He's showed in the preseason he may have the most upside of any of the backups if Gore were to get hurt.