Jackson suffered the injury on the first play of the Redskins' second series, when he ran a deep route on an overthrow by quarterback Kirk Cousins.
DeSean Jackson, who missed the entire preseason with a shoulder injury, was knocked out of Sunday's season opener with a hamstring injury. Troy Taormina/USA TODAY Sports
"Any time you lose a guy that runs a 4.25 40, it damages some of your play-action game," Gruden said. "The first one we threw to him, he had a step [on the corner] and I believe he would have caught it if he didn't pull his hammy.
"It's a great throw by Kirk, and that's the last we saw of him -- and we had another seven or eight [plays] built in to clear out and get DeSean across the field. It was a big loss for us."
The Redskins initially listed Jackson as questionable to return before eventually downgrading him. With Jackson sidelined, the Redskins lose their best deep-ball target. Second-year receiver Ryan Grant replaced him in three-receiver sets but lacks the deep speed to threaten defenses. Jackson led the NFL with 13 catches for 40 or more yards last season.