Ryan O'Halloran of the Denver Post added the Broncos will save $11.87 million against the 2021 cap.
The move comes two weeks after the Broncos released veteran cornerback A.J. Bouye to save $11.7 million against the salary cap.
Denver projects to have around $48 million in cap space once Casey's release becomes official, per Spotrac. That number could go even higher if the team declines Von Miller's $22.25 million option for next season by the March 16 deadline.
Mike Klis of 9News reported on Feb. 17 that the Broncos haven't made any decisions about Miller's contract.
Casey was traded to Denver last offseason after spending the first nine seasons of his career with the Tennessee Titans. The 31-year-old was named to the Pro Bowl five consecutive years from 2015-19.
A torn biceps limited Casey to just three games with the Broncos in 2020. He had 14 combined tackles and two quarterback hits prior to suffering the injury in Week 3 against the Tampa Bay Buccaneers.