The Broncos placed Simmons on injured reserve Wednesday. He was injured in Denver's 23-0 win over the Jets on Sunday, their first win in 70 days.
Simmons landed awkwardly when he came down on Marshall's right foot and had to leave the game. He was replaced by fellow second-year safety Will Parks.
Coach Vance Joseph called the injury fluky, saying, "What do you say to Justin? Don't celebrate? Don't have fun?"
Simmons had hoped to miss just one game, Thursday night's visit to Indianapolis.
After showing flashes as a rookie, Simmons supplanted T.J. Ward as Denver's starting strong safety this summer and ranked third on the team with 63 tackles. He also had a sack, five pass breakups and two interceptions, including a pick-6.