Knehr was optioned to Triple-A El Paso on Wednesday.
Knehr was called up to make a spot start in Tuesday's doubleheader against the Rockies, so his move back to El Paso was expected. The right-hander allowed two runs over 3.2 innings and has a 1.50 ERA, 0.75 WHIP and 8:2 K:BB across four big-league outings this year.