Mitchell is one of six different players to start at left or right tackle for the Jets, who started losing players in training camp.
Coach Robert Saleh declined to disclose the reason for putting Mitchell on the NFI list, saying, "I'm not going to get into specifics right now because there are a lot of things we're trying to sort out."
Typically, players go on the NFI list if they have an illness or medical condition, or if they suffer an injury away from the team facility.
Mitchell, a fourth-round pick from Louisiana, made his fifth start Sunday but was benched in the second quarter of the Jets' 27-22 loss to the Minnesota Vikings. He was replaced by Fant. Saleh said he made the change because Mitchell, who allowed a sack, was struggling in the game.
Chances are, the Jets would've kept Fant in the lineup for Sunday's important AFC East game in Orchard Park, New York, but the Mitchell development hurts their depth.
Veteran journeyman Mike Remmers, who has yet to play an offensive snap, becomes the backup swing tackle. Veteran guard Laurent Duvernay-Tardif, on leave from his medical residency in Canada, was elevated to the active roster from the practice squad.
The Jets' run of bad luck started early in training camp, when right tackle Mekhi Becton suffered a season-ending knee injury. In Week 7, Alijah Vera-Tucker, a guard who switched to right tackle, was lost for the season with a torn triceps.