Johnson, one of the Longhorns' top playmakers on offense, suffered the injury on Texas' first possession during the Longhorns' 40-21 loss at BYU and did not return. Coach Mack Brown did not disclose the severity of the injury during his Monday news conference but did rule Johnson out for Saturday.
The sophomore running back/wide receiver scored two touchdowns in Texas' season opener against New Mexico State and was slated to play a significant role against BYU before being sidelined.
"When you lose a guy that's involved in packages, like Daje, obviously you've got to find somebody else to put in that place, and certain things immediately go out the window," Texas offensive coordinator Major Applewhite said after the BYU game.
The Longhorns (1-1) also don't know if quarterback David Ash will be available against Ole Miss (2-0). The junior left the BYU game in the fourth quarter with head and right shoulder injuries, and his status is considered day-to-day while UT trainers continue to evaluate him.
If Ash is unavailable, Brown said senior Case McCoy will start and true freshman Tyrone Swoopes, who seemed likely to redshirt, would prepare to be his backup. McCoy threw for 62 yards on 5-of-10 passing against BYU.
"Tyrone practiced with the second team, and Case practiced with the first team last night," Brown said. "David wasn't out there. Case has shown the ability to win at Kansas late. He's shown the ability in one of the toughest games we've had on the road and beat A&M. He's just got to take care of the ball better."
McCoy has made six career starts, including a loss at Kansas State to end the 2012 regular season when Ash was injured.