Mitchel (hamstring) has been released by the Colts after reaching an injury settlement with the team, George Bremer of The Herald Bulletin reports.
Mitchel missed all of last season due to injury, and entered this season on the IR. He injured his hamstring in the team's final preseason game. The 24-year-old has yet to play in a regular season game.
Miller was placed on the active/no-football list with an undisclosed injury on Tuesday.
The severity of the injury is still unknown, but Miller, a rookie undrafted free-agent, will now miss the beginning of his first training camp. Fellow tight end Darion Griswold was placed on the PUP list, leaving the Colts with five healthy tight ends to open up training camp.
Jones will be suspended for the first four games of the 2016 season for violating the NFL policy on PEDs, Ian Rapoport of NFL.com reports.
Jones missed the entire 2015 season due to torn ligaments in his ankle and did not participate in spring practices. He may have been sidelined to start the season even without the suspension, but this still hurts Indy's depth on the defensive line.