Day is a team captain and is sixth on the team with 38 tackles and leads the team with 7.5 tackles for loss. It's unlikely he'll be able to play against USC. Kelly says backup defensive lineman Daniel Cage also is out for the Irish (7-3) against Louisville (7-3) with a knee sprain.
Kelly said he will have to shuffle the line, saying Justin Utupo, Grant Blankenship and others could see more playing time. The Irish defense has struggled in recent weeks, giving up 30 or more points for five straight games for just the second time in school history.