Mack (undisclosed) did not participate in June minicamp, Stephen Holder of The Indianapolis Star reports.
While there's no indication the injury is significant, it isn't ideal for a rookie to miss any time during the offseason program. Mack still figures to be ready for training camp, where he'll compete with 27-year-old Robert Turbin and 2016 UDFA Josh Ferguson for backup work behind 34-year-old Frank Gore. The fourth-round rookie is the only one of the bunch with any real upside as a runner, but Turbin's combination of size, experience and pass-blocking ability makes him the favorite to earn the No. 2 spot on the depth chart. There could be room for three players to contribute each week, as the Colts seemingly hope to ease Gore's workload in what could be his final season.