The injury is a Grade 2 shoulder separation, according to the report.
Jackson suffered the injury after running into a blocking sled while finishing running a route on the first play of 1-on-1 drills. The Redskins have yet to officially announce a diagnosis.
Jackson, 28, caught 56 passes for 1,169 yards and six touchdowns last season, his first in Washington after six years with the Philadelphia Eagles. He led the league with 20.9 yards per catch and with 13 catches for 40 yards or more. However, his 56 catches didn't crack the league's top 50 for total receptions.
The three-time Pro Bowl wideout suffered fractured ribs in Week 12 of 2013 and missed the remainder of the season. He bruised a shoulder after falling in a Week 2 game last season. Heading into training camp he was set to serve as Redskins quarterback Robert Griffin III's top target.
- Jeremy Woo and Erin Flynn