The Athletics acquired Johnson from the Phillies on Monday in exchange for outfielder Colby Thomas.
Johnson has yet to find much success in the majors, putting up a 7.18 ERA and 37:21 K:BB over 31.1 frames covering parts of three seasons. However, he's a hard thrower who holds a 2.17 ERA and 40:11 K:BB across 29 frames this season at Triple-A Lehigh Valley. Johnson might get a chance to pitch high-leverage innings as part of a patchwork Athletics bullpen.