Coach Brian Kelly says the 6-foot-5, 315-pound senior has a torn medial collateral ligament and will undergo surgery in the next few days. Kelly calls it a freak injury, saying Jones was standing and another player fell and rolled up on him during an 11-on-11 drill in practice Friday.
Jones watched practice Saturday with a brace on his knee.
Jones was a returning starter who missed the final two games of last season after undergoing surgery on his left foot. He was ninth on the team in tackles with 40, including 1 1/2 sacks.
Kelly says freshman Jerry Tillery and sophomore Daniel Cage are the likely replacements for Jones.