The Washington Post's Gene Wang and Scott Allen discuss the loss and break down Kirk Cousins's performance. (Thomas Johnson/The Washington Post)

Coach Jay Gruden had no quibble with DeSean Jackson missing much of the Washington Redskins’ optional workouts this spring.

And when an Aug. 6 shoulder injury that was expected to sideline the wide receiver for one to two weeks stretched into a third week, Jackson himself announced that he would be best served by extending his recovery through the preseason as well.

“Won’t have to worry about me at all,” Jackson told reporters Aug. 25, dismissing questions about his readiness for the Sept. 13 season opener without benefit of a preseason tuneup. “I’ll be the same person I’ve always been: making plays and being the guy that brings the energy to this team.”

Jackson’s contribution lasted less than one quarter Sunday at FedEx Field, where the three-time Pro Bowl honoree grabbed the back of his left thigh after streaking down the sideline in pursuit of a deep ball, a Miami cornerback at his heels.

Gruden on Monday confirmed that Jackson had “pulled a hamstring” and announced he would miss three to four weeks, which puts his return at the Oct. 11 game at Atlanta or Oct. 18 at the New York Jets.

“Could be shorter, but you never know with hamstrings,” Gruden said.

Asked whether the fact that Jackson had skipped the preseason and, in effect, gone from zero to 60 at kickoff of Sunday’s game, which the Redskins lost, 17-10, Gruden conceded the possibility.

“It very well could have, but we don’t know that,” Gruden said. “He just went for a deep ball and pulled it. Obviously, you like to have guys all throughout training camp, but the shoulder limited him. He still was able to do a lot of running in that time, so I don’t think it really did. I think it’s a thing that happens to a wide receiver now and then.”

If there’s one position at which the Redskins are well stocked, it’s wide receiver, with youngsters Ryan Grant, Rashad Ross and rookie Jamison Crowder waiting for opportunities behind veterans Pierre Garcon and Andre Roberts. But none has the rare breakaway speed of Jackson or the body of work that dictates defensive coverages.

Grant, a second-year player from Tulane, stands out for his route-running precision. Ross, a former Arizona State track star who goes by the nickname “The Rocket,” comes closest to Jackson for raw speed. And the 5-foot-8 Crowder earned a reputation at Duke for fearless, reliable catches in traffic.

But none represents an even swap for Jackson, 28, whose 20.9 yards-per-catch average led the NFL last season.

“You hate to lose a star, especially with his speed,” Gruden said. “We feel good about the receivers that take his place, but nobody can substitute him for that burning speed that gets downfield and scares safeties and corners to death.”

Once Jackson exited Sunday’s game, Gruden reined in the offensive game plan, with no use for the seven or eight plays he had drawn up for the speedster.

And going forward, Gruden conceded, opposing defenses will take a more aggressive approach, knowing they don’t have to account for Jackson.

“It enables them to play a little bit tighter coverage when he’s out of the game,” Gruden said. “Safeties creep up a bit. It’s a big loss for us, no question about it, and now we’ll have to ask Ross to step up and play, and Ryan Grant and Crowder.”

Jackson’s injury occurred on the first play of the Redskins’ second offensive series. Quarterback Kirk Cousins uncorked a deep throw down the right sideline, and Jackson outraced cornerback Brent Grimes in an effort to reel it in.

The ball fell beyond his grasp, and Jackson grabbed his hamstring.

From Gruden’s perspective, it was a great throw that fell incomplete because of a split-second delay by Jackson, whose feet got tangled trying to separate from Grimes.

“Had he not pulled [the hamstring], would he have caught it?” Gruden asked rhetorically. “I don’t know. But I thought it was an excellent throw.”

Among those watching on TV was orthopedic surgeon David Geier, founder of Sports Medicine University, who said he knew the injury was significant the moment Jackson grabbed his hamstring.

Hamstring injuries can sideline athletes anywhere from one to eight weeks, Geier said in a telephone interview, depending whether the muscle is strained, partially torn or completely ruptured. Gruden didn’t specify the severity of Jackson’s injury.

Moreover, Geier said, once an athlete injures a hamstring, there’s “a fairly high recurrence rate.” That’s why many trainers take a cautious approach in clearing players to return.

Asked whether Jackson’s relative inactivity in the preseason could have been a contributing factor, Geier said he couldn’t say but noted that hamstring injuries were more common during training camp and the beginning of the preseason than later in the season, when athletes are fully conditioned.

“You see them a lot with the first real aggressive physical activity — be it training camp or in a return from other injuries, so there probably is something to getting in game shape and getting used to the sudden spring that you can’t replicate running on a treadmill or on a track,” Geier said. “I don’t say that in a blaming sense. But you see more of these in the preseason than in Week 14.”