UCLA linebacker Myles Jack will miss the rest of the season with a knee injury, the most devastating blow yet for a Bruins’ defense that had already lost two starters.

Jack was arguably the most versatile player on the roster, a 6-foot-1, 245-pound athlete who was capable of matching up one on one with wide receivers and returning kicks. No other Bruin is capable of replicating what he provided to a defense that, through three weeks, ranked top 20 nationally in scoring defense (14.0 points) and yards allowed per play (4.39).

Head coach Jim Mora would not say whether or not Jack had torn his ACL, only calling it a “significant knee injury.” Jack suffered the injury late during Tuesday’s practice, and had surgery later in the day.

The All-Pac-12 second-team linebacker was projected as a first-round pick before his injury. He took out an insurance policy in April 2014, one that Yahoo! Sports reported to be worth more than $5 million and accounted for injuries affecting his NFL draft stock.

UCLA also lost starting defensive lineman Eddie Vanderdoes to a torn ACL in a season-opening win over Virginia, and starting cornerback Fabian Moreau to a foot fracture this past weekend.