USC linebacker Jabari Ruffin, who appeared on track to possibly start, will be sidelined for the season because of a torn knee ligament, the school announced Sunday night.
Ruffin, a third-year sophomore, was injured after intercepting a pass during a morning workout.
"This is very unfortunate news about Jabari, but I know he will rehab well and come back strong next year," Coach Steve Sarkisian said in a statement. "And, I know our team will step up in his absence."
The 6-foot-3, 240-pound Ruffin, who came to USC from Downey High, was enjoying a productive training camp.
He intercepted a pass by Max Browne, but was injured when tackled during the return. Ruffin was helped to the sideline by trainers and spent the rest of practice with an ice pack on his knee.
Senior J.R. Tavai, third-year sophomore Scott Felix and sophomore Quinton Powell are other outside linebackers competing for starting roles.
Ruffin is the second player to suffer a season-ending knee injury. Defensive lineman Kenny Bigelow was injured during a players-only workout in July.
Sarkisian has spoken of managing a roster that is still depleted in the aftermath of NCAA sanctions.
Last week, defensive lineman Antwaun Woods suffered an elbow injury that could sideline him for a few weeks.
Sarkisian said Sunday that defensive lineman Cody Temple suffered a concussion during the Trojans' first full-pads workout Friday.
On Sunday, receiver Darreus Rogers rested a sore Achilles' tendon and multipurpose player Adoree' Jackson sat out much of practice after another player stepped on his foot. Defensive lineman Leonard Williams was held out after taking a hit to his left shoulder. Williams is recovering from right shoulder surgery.
Sarkisian said all players would be evaluated but he did not expect any of Sunday's injuries to be major.
Ruffin's, however, ended his season.
Agholor the elder
Nelson Agholor spent his freshman season as USC's No. 3 receiver behind Robert Woods and Marqise Lee.
Last season, he was the second option until Lee suffered a knee injury in the fifth game against Arizona State.
After averaging 16.4 yards a catch and scoring eight touchdowns as a sophomore, the 21-year-old junior is now the leader of the receiving corps.
"I'm just trying to focus in and make all the plays that come my way," Agholor said Sunday after a morning practice.
Agholor has made multiple outstanding catches during training camp, teaming with quarterback Cody Kessler on several touchdown pass plays.
"I know where he's going to be every time on the field and, no matter what route it is, I know which way he's going to run it," Kessler said.
Agholor also has led by example, helping freshmen such as JuJu Smith, Jackson, Rahshead Johnson and Ajene Harris.
Agholor acknowledged a solid start to training camp, but insisted that improvement was needed. "I've done well," he said, "and I have to continue to pick it up."
Soma Vainuku is listed as a fullback, but in USC's new fast-paced offense he does not figure to be utilized much in the position's traditional mold.
The junior from Eureka is playing a utility role, working at running back, tight end and also on special teams.
"Fullback and tight end kind of go hand in hand," Vainuku said.
Last season at Colorado, Vainuku rushed for 70 yards and a touchdown, caught two passes and blocked a punt into the end zone for a safety in a 47-29 victory.
He said he still calls on lessons learned from former Trojan Rhett Ellison, whose versatility as a tight end and fullback helped launch an NFL career.
The Trojans, in the first of six double-day workouts during the next two weeks, also practiced in the evening. The evening workout was closed to the media
After meeting with the staff Saturday, Sarkisian said there was "some thought" of having freshman receiver Smith play nickel back and "getting a look" at Johnson at cornerback.
After the morning practice, Sarkisian participated in the "Ice Bucket Challenge" to raise awareness for ALS. With players surrounding him, Sarkisian was doused with ice water and then challenged Seattle Seahawks Coach Pete Carroll to do the same.