Mushinski was optioned to Triple-A Sugar Land on Sunday, Chandler Rome of the Houston Chronicle reports.
The 26-year-old was reinstated from the 15-day injured list Thursday after missing time with an elbow injury, and he'll head to the minors with Ryan Pressly returning from the paternity list. Mushinski delivered a scoreless inning Saturday and has given up three earned runs with an 8:3 K:BB across 7.1 innings for Houston this year.