Senior Case McCoy will start for the Longhorns (2-2) against the Cyclones (1-2).
Ash has missed part or all of Texas' previous three games after being injured in the second half of a loss at BYU on Sept. 7. He missed Texas' loss to Mississippi the next week with concussion-like symptoms and was told to stay away that night to avoid the crowds and lights of the stadium.
Ash returned to play the first half of Texas' win over Kansas State on Sept. 21. He didn't return for the second half and the school announced he was being evaluated for a head injury.