Addison reportedly injured his left knee during a non-contract drill.
It is not clear how long Addison will be out, but he could miss the season. He is the Ducks' top returning receiver. Oregon already lost two of its top three receivers from last year, Josh Huff and Daryle Hawkins, who are graduating.
Addison had 61 receptions for 890 yards with seven touchdowns last season. He also returned two punts for scores.