Beckman said in a news release late Sunday that the redshirt sophomore quarterback broke his fibula Saturday in the Illini's 38-27 loss to Purdue.
Lunt limped off the field in the fourth quarter and didn't return. He said after the game that he had a calf injury he believed he initially suffered in September in the loss to Washington.
Beckman said in the release he is disappointed for Lunt, who is having a strong season. Lunt is in the top 20 in the nation in passing yards with 1,569 and touchdowns with 13.