The injury will require surgery and Mitchell could miss 4-6 weeks, NC State coach Dave Doeren said after the game.
Mitchell, who transferred from Arkansas, directed the Wolfpack to touchdowns on the first two possessions before he was hurt when he was stopped on a third-and-1 keeper on his third series. Mitchell headed to the locker room.
He returned to the sideline without his pads late in the first half, using crutches and wearing a protective boot on his left foot.
The school announced shortly before kickoff that Mitchell would start the first game. He had been competing with Colorado State junior transfer Pete Thomas, who took over after Mitchell's departure.
NC State won 40-14 in Doeren's debut.