NFL coaches emphasize the third exhibition game as the last real tuneup for the first-stringers before the regular season begins, but the Vikings need to be cautious with Jackson's sprained right knee. He was hurt last week at Baltimore.
He warmed up his arm before the game, but wore shorts and a baseball cap while the rest of the team went through drills.
"I maybe could've played," Jackson said. "I'm just trying to be precautionary right now, not trying to go out there and push it."
Jackson sat down with Vikings coach Brad Childress about 40 minutes before game time. The coach asked the quarterback to give him a straight-up assessment of how he felt. When Jackson said he still felt some pain moving laterally, Childress decided to play it safe.
"In fact he could've played and he could've played a certain way with a certain menu of plays and probably had to stay in the pocket, but that's not the prudent thing to do," Childress said. "There may be a time when he has to play the game that way, but I thought he did a good job of pushing to that and he'll get better as we go along."
Jackson said he may not be 100 percent by the time the Vikings open the regular season Sept. 8 at Lambeau Field against the Packers, but there is "no doubt" he will play in the game.
Gus Frerotte started in Jackson's place and was 13-for-19 for 133 yards and an interception in the 12-10 loss.
Rice has fought a virus the last few weeks and has not practiced much. Berrian is bothered by a sore toe.