The Seahawks made the move to help offset a salary-cap crunch after reaching long-term extensions with quarterback Russell Wilson and linebacker Bobby Wagner, a source told ESPN NFL Insider Adam Schefter.
McDaniel, 30, was set to make $2.5 million in base salary this season and was scheduled to become a free agent in 2016. The nine-year veteran has started in 29 of Seattle's 32 regular-season games over the past two years.
Seattle signed Wagner to a four-year extension worth $43 million Saturday, a source confirmed to ESPN, making him the highest-paid middle linebacker in football.
Wagner's deal came one day after the Seahawks retained Wilson with a four-year extension that, according to sources, is worth $87.6 million, including $31 million in guarantees.