Tampa Bay also announced on Tuesday that it had signed quarterback Rudy Carpenter from the Dallas Cowboys practice squad.
The Bucs also released reserve cornerback Mike Mickens. The team filled his roster spot by signing receiver Terrence Nunn from New England's practice squad.
Leftwich opened the season as the starting quarterback, but was replaced by Josh Johnson after three games. Rookie Josh Freeman has since become the starter, and Leftwich had been listed as third on the depth chart.
Carpenter signed with the Cowboys in May as an undrafted free agent out of Arizona State.