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 extensionworth $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.
The Seahawks also are facing a contract dispute with star safety Kam Chancellor, who is holding out from the start of training camp because of his displeasure with his current deal.
Seahawks release McDaniel
ESPN Insider NFL columnist Mike Sando discusses why the Seahawks are releasing defensive tackle Tony McDaniel.