Mengden will be called up and start Saturday's game in his major league debut, Jane Lee of MLB.com reports.
Mengden has been dominant in the minors this season, with a 1.19 ERA in 11 starts between Double-A Midland and Triple-A Nashville. He will be another name to insert into the mess that is the current Athletics rotation. Rich Hill was placed on the DL with a groin strain while Jesse Hahn was optioned after his latest bad start. Zach Neal was also called up, but there's no indication he'll be put in the rotation.