TMZ Sports has learned Miller Moss -- the star quarterback who helped lift the Trojans to an upset win over No. 13 LSU this weekend -- was investigated by USC a little less than three years ago ... after he was involved in a feud with his roommate.
The probe occurred sometime in the spring of 2022 -- just after the signal-caller had finished his first season at Southern Cal.
The school tells us it could not get into the specifics of the matter due to legal reasons -- but in a statement released on Moss' behalf, the redshirt junior QB said he was remorseful for the behavior that apparently sparked the investigation.