Cook is dealing with the lingering effects of a knee injury from a hit he took in the first half of this past Saturday's game against No. 15 Kansas State, in which he threw for 356 yards and two touchdowns to lead the Tigers to a 30-27 win.
Cook spent most of last season playing through a shoulder injury that required offseason surgery, as he tore his labrum against Kansas State last season.
Cook is coming off one of the best games of his career. He began the season sharing snaps with Horn in the South Dakota Coyotes game, but he has since played well, including delivering Missouri one of the program's biggest wins in recent years Saturday when kicker Harrison Mevis booted a game-winning 61-yard field goal to topple the defending Big 12 champions.
Before the game, Cook received some boos in pregame warmups. He was staunchly defended by coach Eliah Drinkwitz.
"He went out there and played his butt off for this university and this team," Drinkwitz told reporters. "They need to get behind him. We need to get behind the young man. You want to boo me? Fine. You're going to boo the starting quarterback? Bull crap. I'll say it again. Should never happen."
Missouri (3-0) is off to its best start since 2018 after wins over South Dakota, Middle Tennessee and Kansas State.
Missouri hosts Memphis (3-0) on Saturday (7:30 p.m. ET, ESPNU) in a matchup of undefeated teams.