The Mariners designated Knizner for assignment Tuesday.
Knizner will cede his spot on 40-man roster to Mitch Garver, who beat him out for the No. 2 catcher job coming out of spring training. A lifetime .211/.281/.316 hitter over parts of seven MLB seasons, Knizner could attract interest on the waiver wire from other teams looking to upgrade their backup catcher spot ahead of Opening Day.