Wilson will redshirt the 2012 season.
A true freshman, Wilson suffered the injury on Tuesday during noncontact drills, Kiffin said. It's the second torn ACL Wilson has suffered since originally signing with the Trojans in February 2011.
He underwent surgery on the right ACL last August after tearing it in offseason work in his hometown of Corona, then grey-shirted last season and enrolled at USC in January.
The Trojans are now down to 70 healthy scholarship players on their roster, with the academic status of three players not yet determined and three others likely out for the 2012 season.
Wilson is the second defensive end to go down long-term. Senior Devon Kennard tore his pectoral muscle last month and is expected to be out until at least November or December, if not the entire season.
Pedro Moura covers USC for ESPNLosAngeles.com