With shoulder pads removed, he eventually made his way off the field.
USC head coach Lane Kiffin said after practice he did not know Lee's status, "He fell over there, they took him in to check it out, that's about all I know," Kiffin said.
Kiffin expected to learn more after the conclusion of the press conference, "When we get in there, they'll tell me if he is getting x-rays or something," he said.
Lee carried the weight of USC's offense in 2012, being named the nation's top receiver. He caught 118 passes for 1,721 yards including 14 touchdowns.
Kiffin said it's a "glass half empty" view to think Lee might not be available this season, but said if that's the case "somebody will have to step up.
"Darreus Rogers is playing well as the third guy right now and he'd have to step up and play, like what's happened here before. Next guys up."
Keep it on SCPlaybook.com for the latest on this developing story.