Muller was optioned to Triple-A Gwinnett on Wednesday.
The southpaw was productive during Tuesday's start in Washington, allowing two runs on six hits and a walk while striking out four in 4.2 innings. However, he'll head back to the minors as part of a move to make room for Silvino Bracho on the active roster. Muller spent most of the 2022 season at Gwinnett and posted a 3.41 ERA and 1.18 WHIP in 134.2 innings over 23 starts.