Stewart was optioned to Triple-A Oklahoma City on Tuesday, Fabian Ardaya of The Athletic Los Angeles reports.
Stewart will head back to the minors for the time being with Clayton Kershaw (biceps) expected to return Thursday and bump him from the rotation. It's unclear if Stewart will remain stretched out in the minors or rejoin the big club in a long-relief role when he's eligible to return. He owns a 4.61 ERA across 13.2 major-league innings (two starts, three relief appearances) and a 2.08 ERA across 21.2 Triple-A frames (five starts).