The Athletics transferred Hernaiz (ankle) from the 10-day injured list to the 60-day IL on Wednesday.
The transaction frees up a spot on the 40-man roster for right-hander Aaron Brooks, who was called up from Triple-A Las Vegas ahead of his scheduled start Wednesday versus the Astros. Hernaiz suffered a severe left ankle sprain last week and now won't be eligible to return until early July. Max Schuemann has since taken over as Oakland's everyday shortstop in his stead.