The Rangers optioned Knizner to Triple-A Round Rock on Monday.
Knizner lost his spot on the 26-man active roster after the Rangers acquired Carson Kelly from the Tigers on Sunday to serve as the new No. 2 catcher behind Jonah Heim. Knizner has slashed a lowly .167/.183/.211 with one home run and nine RBI across 93 plate appearances in the big leagues this season.