Jackson gained 11 yards on a designed run, but came up holding his right shoulder and upper chest. Coach Pete Carroll said after the game that Jackson had a pectoral muscle problem and will undergo an MRI exam back in Seattle.
Jackson was replaced by Charlie Whitehurst, who led Seattle to a 36-25 victory. Jackson was 15 for 22 for 166 yards, a touchdown and an interception in the game.
Seattle also lost linebacker Leroy Hill with a hamstring injury in the fourth quarter. Tight end Zach Miller sustained a head injury and will undergo further examination this week, when the Seahawks have a bye. Linebacker Jameson Konz strained a knee.
After the game, the Giants said guard Chris Snee was taken to a hospital for observation with a concussion.