Mack (shoulder) donned a non-contact jersey and took part in drills during Thursday's practice, Zak Keefer of The Indianapolis Star reports.
It's a step in the right direction for Mack, but unless he's cleared to take contact during the team's final practice of the week Friday, his chances of suiting up in Week 4 against the Seahawks appear slim. Mack's probable absence would result in Robert Turbin serving as starter Frank Gore's primary backup, while the recently promoted Matt Jones would function as the team's No. 3 running back for the second straight week.