Projected starting defensive tackle Kenny Bigelow Jr. was carted off Howard Jones Field on Thursday during the USC's fifth spring practice.
Bigelow went to the ground clutching his right knee during a portion of practice when they were running plays. As soon as the play ended, staff members and players emphatically yelled for the trainers assistance. The 6-foot-3, 290-pound redshirt junior was helped to a training table, where his knee was examined.
A doctor was later summoned before Bigelow was carted off the field.
"We'll MRI that tonight and hopefully know by Saturday what's going on right there," USC Coach Clay Helton said.
"We'll all be saying our prayers tonight. He's very much a leader of our team and we need him."
Bigelow is the only upperclassman among interior defensive lineman on the current roster after USC graduated five seniors, including all three starters. In his first season as a Trojan, Bigelow played in 13 games in 2015 as a backup, making 10 tackles, including three sacks.
The high school All-American redshirted in 2013 and missed all of the 2014 season after tearing the anterior cruciate ligament in his right knee -- the same one that was being looked at on Thursday.
Other injury notes from USC's fifth spring practice:
--Junior wide receiver JuJu Smith-Schuster was held out of practice because of a tight hamstring.
--Freshman wide receiver Michael Pittman has a crack in the same collarbone he broke in January and will not participate in contact drills the remainder of the spring.
--Sophomore defensive lineman Noah Jefferson has a lower-back injury that has caused him to miss the last two practices. An MRI exam came back negative, but USC is having Jefferson undergo an additional CT scan.
--Sophomore tight end Tyler Petite is going through concussion protocol. Helton hopes to have him back next week.
--Helton said sophomore linebacker Osa Masina is "getting close" to returning from a hamstring injury that has not allowed him to participate this spring.