Mack took the bulk of second-team reps at Wednesday's practice, George Bremer of The Anderson Herald Bulletin reports.
While seemingly destined to open the season third on the depth chart, Mack at least has a chance to get extended run with the second unit while the Colts use Robert Turbin with the starters to avoid overworking 34-year-old Frank Gore. Given Gore's age and Turbin's uninspiring NFL track record, the fourth-round rookie could earn a change-of-pace role, providing some much-needed explosiveness from the Indy backfield. The Colts hope Mack will eventually be Gore's successor in the lead role.