Leary was sliding to end a quarterback run when Duke safety Lummie Young hit him in the head. Leary's ankle twisted awkwardly under him, and he stayed down on the field for several minutes. He was carted off the field with an air cast on his left leg.
"It doesn't look like we'll have him for a while," coach Dave Doeren said after the game. "He's a tough kid and hate it for him to get injured like that because I know how much this game means to him, this team means to him."
Leary later returned to the sideline in the fourth quarter wearing a walking boot and on crutches.
Young was ejected for targeting.
After being named the starter in the offseason, Leary was unable to start the first two games because he missed practice time during a contact tracing quarantine for the coronavirus. He won the last two games he started.
Bailey Hockman came on in relief of Leary and helped lead the Wolfpack to a 31-20 victory.