Mack is dealing with a shoulder injury and missed a third consecutive practice Thursday, Zak Keefer of The Indianapolis Star reports.
While likely stuck behind Frank Gore and Robert Turbin, the fourth-round rookie could at least make a case for a change-of-pace role this preseason if his shoulder issue isn't serious. Mack has already made a strong impression on coach Chuck Pagano, who recently said that the rookie back "jumps off the tape."