Baylor officials didn't elaborate Sunday, but they confirmed that Johnston had a season-ending injury.
Johnston got hurt in the fourth quarter of Saturday's 33-30 double-overtime win over Texas Tech, when the Bears stayed undefeated. He limped off the field and never returned after his interception deep in Baylor territory.
His 58 tackles this season are 28 more than any other Baylor player, and he is third in the Big 12 Conference with 9.7 tackles per game. He had 10 tackles Saturday for his fourth consecutive double-digit game.