Coach Lane Kiffin announced the probability Monday after practice, saying he had spoken with Prater's parents about the 14th-ranked Trojans' plans for the touted freshman.
Prater was among the nation's top recruits when he committed to the Trojans last year out of his native Illinois. He enrolled early at USC this year, but his play in training camp has been limited by various lower-body injuries.
Prater isn't ready to play in USC's season opener at Hawaii on Thursday night.
Kiffin says Prater is likely to sit out the season unless other receivers get injured.