If the Broncos don't decline his 2021 option before March 17, the linebacker will be guaranteed $7 million, leaving them another month to evaluate the roster.
Miller would have a $22.2 million cap hit for next season if Denver picks up his option, but the team can save $18 million by declining it, per Spotrac.
The Athletic projected Miller could be a salary-cap casualty this offseason.
The 31-year-old missed the 2020 season because of a dislocated peroneal tendon in his ankle, just the second time he has missed more than two games in a season.
Miller earned his eighth Pro Bowl selection in 2019 after totaling eight sacks with 46 tackles, 10 for a loss.
He has made the All-Pro First Team three times and was a major reason the Broncos won Super Bowl 50 in the 2015 season. Miller's 106 career sacks rank 25th in NFL history, more than anyone who played in 2020.
Though he could likely still contribute to an NFL team in 2021, the Broncos need more help than a single player can provide after a 5-11 season. The squad could let Miller go and focus on the future with younger pass-rushers like Bradley Chubb and Malik Reed.