Stewart, who transferred from Texas A&M, had 48 catches for 613 yards and five touchdowns this season. He had been the Ducks' second-leading receiver behind Tez Johnson.
During Oregon's 32-31 win over Ohio State in October, Stewart had his best game of the season, totaling 149 yards on seven catches and one touchdown.
Starting running back Jordan James also exited the game in the second quarter with an apparent head injury. James went back to the locker room and was ruled out of the game coming out of halftime, according to ESPN's Holly Rowe.
Before the injury, James had seven carries for 14 yards. The junior carried the ball 226 times for 1,253 yards and 15 touchdowns this season and had been a key part of Oregon's offensive attack.