Illinois sports information assistant director Kent Brown said Buchanan's jaw has been wired shut and he is expected to see a specialist later this week. Brown said the hope was for Buchanan to be ready to play for the team's preseason camp.
Illinois coach Tim Beckman said Wednesday he was unaware how the injury occurred.
"We're still in the process of exactly how it happened," Beckman said.
Beckman said Buchanan was currently at his family's home and was expected to return to campus on Saturday or Sunday.
Buchanan, who is 6 feet 6, 240 pounds, was fourth in the Big Ten last season with 7½ sacks. He also had 64 tackles, 13½ tackles for loss and four hurries. He was named second-team all-Big Ten by coaches and media.