Houser exited his outing Saturday against the Athletics with a trainer, Curt Hogg of the Milwaukee Journal Sentinel reports.
The nature and severity of Houser's injury are not yet clear. He was expected to open the year in the bullpen but looked like one of the top options for a spot start in the absence of Aaron Ashby (shoulder). If Houser misses time as well, Bryse Wilson could fill that role instead.