Atlanta optioned Muller to Triple-A Gwinnett on Sunday.
Muller's demotion likely leaves Tucker Davidson as Atlanta's No. 6 starter, should the club elect to expand beyond the five-man rotation setup it ran out for most of 2021. As a rookie last season, Muller made nine appearances (eight starts) for Atlanta, posting a 4.25 ERA, 1.25 WHIP and 37:20 K:BB in 36.2 innings.