Knapp was designated for assignment by the Pirates on Monday, Mike Persak of the Pittsburgh Post-Gazette reports.
Knapp saw sporadic playing time while serving as the Pirates' backup catcher early in the season, and he hit just .129 with a double, two runs and two RBI over 11 games during the first month and a half of the year. He'll lose his spot on the 40-man roster after Tyler Heineman was claimed off waivers from the Blue Jays on Monday.