Justin Roper will start in the opener against Washington on Saturday in Autzen Stadium. His backups will be Jeremiah Masoli, a sophomore transfer, who led City College of San Francisco to the junior college national title last year, and true freshman Chris Harper. Neither Masoli nor Harper have played in a Division I-A game.
Costa, who will need surgery to repair damaged cartilage, began spring as the overwhelming favorite to run the Ducks' spread offense, but Roper had been surging in recent weeks.
Roper played extensively last year after Dennis Dixon went down with his own knee injury. Roper threw four touchdown passes in the Ducks' 56-21 Sun Bowl victory over South Florida.
Costa first tore ligaments in his knee on Oct. 30. The MRI following his new injury Wednesday was inconclusive over where there is new ligament damage. The status of his ACL and MCL will be assessed during the upcoming surgery. A date has not been set for surgery.
In other news, head coach Mike Bellotti also announced that junior linebacker Kevin Garrett, who had been suspended indefinitely prior to the start of fall camp, has been dismissed from the team.
Ted Miller covers the Pac-10 for ESPN.com and can be reached at email@example.com.