Gruden says Jackson was hurt Thursday when he landed on the shoulder after catching a pass during a joint workout with the Houston Texans.
The speedy receiver missed time last season with an injury to his left shoulder, but still caught 56 passes for 1,074 yards and six touchdowns.
Gruden says cornerbacks DeAngelo Hall and Chris Culliver sustained groin injuries and are listed as day-to-day, and linebacker Trevardo Williams sustained a hamstring injury that will keep him out of action for 1-2 weeks.
Gruden says safety Akeem Davis has surgery on his thumb on Thursday and could return to action as soon as Friday.
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