Johnstone tore his ACL last December during the Ducks' bowl game, and after months of rehab he was hoping to return for the season opener.
The tackle was recently cleared to ease back into practice, but heard a popping sound in his knee during the first week, according to CSNNW. Tests and scans revealed that he had re-torn the ACL in his right knee.
Johnstone will have surgery on Friday, reports CSNNW.
Johnstone was named to the Pac-12 All-Conference Second Team by Athlon following last season. He made 26 consecutive starts on the offensive line for Oregon.
The Ducks' 2014 season begins on Aug. 30 against South Dakota.
- Molly Geary