Coach Brian Kelly said Sunday that while Bars hadn't been diagnosed, "our doctors fear the worst is possible here with the knee," as the injury affected both the ACL and MCL in Bars' left knee.
Bars, the starting left guard and a team captain for No. 6 Notre Dame, sustained the injury midway through the third quarter of a 38-17 win.
"It's devastating for us," Kelly said. "I feel so bad for the kid."
Bars is a fifth-year senior who started 27 games during the past three seasons, mostly at guard with a few at tackle. An ankle injury cost him the second half of the 2015 season.