Dec 30, 2015; San Diego, CA, USA; USC Trojans defensive tackle Noah Jefferson (91) and defensive tackle Kenny Bigelow Jr. (95) work against each other before the game against the Wisconsin Badgers in the 2015 Holiday Bowl at Qualcomm Stadium. Mandatory Credit: Jake Roth-USA TODAY Sports

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USC defensive linemen Kenny Bigelow and Noah Jefferson were sent for medical examinations amid injury concerns.

Only a couple days into their second week of spring practice, the collective USC Football team and coaching staff are holding their breath as Kenny Bigelow and Noah Jefferson face potential injury.

Despite undergoing an MRI on his back that was negative, Trojans head coach Clay Helton said Jefferson will now have a CT scan done.

MRI on Noah Jefferson's back didn't show anything, so they will do an extra CT scan to further examine it. — Shotgun Spratling (@ShotgunSpr) March 25, 2016

Meanwhile, Bigelow, who missed all of the 2014 season after tearing the ACL in his right knee that July, left practice early on Thursday and will have an MRI on his right knee.

USC d-lineman Kenny Bigelow left practice with a right knee injury and did not return. Clay Helton said Kenny will have an MRI tonight — WeAreSC.com (@wearescstaff) March 25, 2016

Jefferson appeared in all 14 games last season as a true freshman. He recored 12 solo tackles and assisted on 11. Bigelow played in 13 games, totaling 10 tackles (seven solo; three assisted).

Lack of pressure from the defensive line was often a point of contention under Justin Wilcox. Along with true freshman Rasheem Green, the tandem of Bigelow and Jefferson are projected to play key roles in defensive coordinator Clancy Pedergast’s attacking defense.