The Tigers announced Wednesday that Kreidler (knee) recently underwent core-muscle surgery, Evan Woodbery of MLive.com reports.
Kreidler was placed on Triple-A Toledo's 7-day injured list April 28 due to knee soreness, but he was cleared to begin a rehab assignment with High-A West Michigan just under a month later. He played in five games in the Midwest League before being pulled off the assignment two weeks ago, presumably on account of the core-muscle injury. Kreidler is in the midst of daily treatment and is taking part in physical therapy following the recent procedure, but he's without a clear timeline to resume playing in games.