The Athletics outrighted Muller to Triple-A Las Vegas after he cleared waivers Wednesday.
Muller has fewer than three years of big-league service time and hasn't been previously outrighted, so he didn't have the ability to reject the assignment to Triple-A after clearing waivers. Before the Athletics moved him off their 40-man roster Tuesday, Muller served mostly in a mop-up role over his 18 relief appearances for the big club, logging a 4.22 ERA, 1.27 WHIP and 35:9 K:BB in 42.2 innings. He could get stretched back out for starting duty as he heads back to Las Vegas.