Johnson will serve as the Athletics' opening pitcher for Sunday's game against the Astros, Martin Gallegos of MLB.com reports.
Sunday is Brady Basso's turn in the rotation, so the Athletics may look to use him in bulk relief once Johnson exits the contest. Johnson has worked exclusively as a reliever this season between stops in the big leagues with the Phillies and Athletics, maxing out at 2.2 innings and 50 pitches over his 27 appearances.