Reich said it's an old injury, possibly from high school, and a broken bone came loose in Wentz's foot.
Wentz felt a "twinge in his foot" when he rolled out and planted to throw late in Thursday's practice, offensive coordinator Marcus Brady said Friday.
Reich said Jacob Eason will continue to receive first-team reps in practice with Wentz sidelined.
Could a first-round pick for Eagles be in jeopardy?
The Colts acquired Wentz during the offseason and reunited him with Reich by giving the Philadelphia Eagles a third-round pick in this year's draft and a conditional second-round pick in the 2022 draft.
The conditional second-rounder can become a first-round pick based on Wentz's playing time.
RELATED: Carson Wentz banner removed from outside Lincoln Financial Field
Wentz needs to play at least 75% of the Colts' offensive snaps for the 2022 conditional pick to convey to a first-rounder.
The pick also could become a first-rounder if Wentz plays at least 70% of the snaps and the Colts reach the playoffs.
Wentz was benched in favor of Jalen Hurts with the Eagles last season after being sacked 50 times and throwing 15 interceptions in 12 games.
Injuries have been an issue throughout Wentz's first five years in the NFL. He suffered a season-ending torn ACL late in the 2017 season. He has played a full season just twice in his career.
RELATED: Eagles rookie WR DeVonta Smith set to miss 2-3 weeks with sprained MCL: ESPN