Rupp signed a minor-league contract with the Athletics on Saturday and was assigned to Triple-A Las Vegas.
Rupp will provide Oakland with extra depth behind the plate in the high minors while top catching prospect Sean Murphy (knee) works back from a torn meniscus. Oakland has received decent production from Josh Phegley and Nick Hundley at the big-league level this season and could get Chris Herrmann (knee) back from the injured list in a couple weeks, so Rupp may have a tough time earning a promotion to the majors even if he performs well in his initial action with Las Vegas.