The A's recalled Muncy from Triple-A Las Vegas on Tuesday.
The 23-year-old was optioned to Triple-A in late July and is now back in the majors with Nick Kurtz (thumb) landing on the injured list. Muncy has a .687 OPS and a 34.3 percent strikeout rate in 48 games this season and is likely to serve as a reserve infielder while up with the big club.